General Information about the T-47/ART-13
Selecting an ART-13 Candidate for Restoration
Deciding How to Power the ART-13
Restoration Hints and Suggestions
"Basket Case" Restoration Project & Typical Restoration Project
Building a Suitable AC Power Supply (includes Schematics)
Setup and Operate the ART-13 Today
by: Henry Rogers WA7YBS/WHRM
photo above: The ART-13 along with a BC-348 receiver installation onboard a Lancaster bomber. Photo from Jerry Proc's website www.jproc.com
|When it comes to vintage WWII military radio transmitters, it's pretty hard to beat the ART-13. It's a potent 100+ watt transmitter that doesn't "weigh a ton" and has the potential to provide first-class audio in the AM mode. On top of that, parts needed for a restoration are usually easy to find and most of the circuitry is not too difficult to work on. Also, I've included construction data, including schematics, on three different ART-13 AC power supplies that I've built. This web-article guide shows how I rebuild and operate ART-13 transmitters. Certainly every restorer/operator has their own techniques and the prospective ART-13 owner should read everything available on these popular military transmitters to help them decide on a project that best suits their abilities and their goals. H. Rogers - May 10, 2011|
|Frequency Coverage and More Accessories - The transmitter frequency range is from 2.0mc to 18.0mc, however many Navy T-47/ART-13 transmitters were equipped with a plug-in Low Frequency Oscillator (LFO) module that allows the transmitter to operate from 200kc to 600kc or 200kc to 1500kc (at somewhat reduced power, CW only.) Early LFOs have a frequency range of 200kc to 1500kc in six ranges while the later LFOs cover 200kc to 600kc in three ranges. The LFO module uses a single 1625 tube. There are some indications that the Navy preferred the 200kc to 1500kc LFO while the USAAF used the 200kc to 600kc LFO. Many versions of the T-47/ART-13 will have a blank plate installed where the LFO module was installed (along with a plug-in resistive load substitute for the LFO's 1625 filament.) After WWII, the USAAF/USAF didn't use the LFO module but the USN still did. This statement is according to the USAF Extension Course 3012 book on "Radio Mechanics" although this book is from the 1950s and may reflect the uses of the LFO at that time rather than during WWII. Many transmitter installations also used a separate antenna tuner and three selectable condensers to allow easier loading into various antenna impedances at lower frequencies. Also most installations on aircraft included a small Remote Control Panel that allowed the pilot to operate the transmitter from the cockpit. There are a couple of different remotes and a few different antenna tuners that could be used depending on the installation requirements. There were at least a couple of different shock mounts available depending on the version of ART-13 and where it was located. Shock mounts provided vibration isolation and elevated the transmitter to allow convection cooling.|
||The Chassis Layout
- To the left is a photo showing the chassis of a
Collins-built T-47/ART-13. This transmitter has the Navy version LFO
installed. Also, this is a fairly early version of the transmitter so
there are some differences when compared to the T-47A/ART-13 versions.
Of note is the lack of an interlock switch which on the early versions
allows you to easily operate the transmitter with the lid off. The
module to the lower right is the Audio Amplifier unit and directly
behind it is the 837 VFO tube. Behind the VFO tube is the FCI/MCW module
and to the left of it are the two 1625 multiplier tubes. The module in
the center of the transmitter is the LFO. In the section at the rear of
the transmitter, to the left side is the modulation transformer from
which its plate leads connect to the two 811 modulator tubes. To the
right of the 811s is the 813 PA tube. The left-center section of the
transmitter contains the matching network and the LF relay (next to the
LFO module.) On the far left is the vacuum TR switch and behind it is
the keying relay. The round ceramic unit in front of the vacuum TR
switch is the inductive pickup for the Antenna Current meter.
T-47A/ART-13 or AN/ART-13A - The somewhat later USAAF T-47A/ART-13 aka: AN/ART-13A version added some minor improvements to the transmitter with a vernier scale on the VFO Fine Tuning, a top lid interlock switch, a different bottom plate with built-in guides for the shock mount and a white ceramic insulator bell on the antenna connection being among the most apparent changes. This model of the transmitter is often found built by various contractors with Stewart-Warner being one of the most often encountered. The contractor identification is most often found on the metal tag mounted on the right side of the transmitter as initials incorporated into the contract number.
|T-412/ART-13B or AN/ART-13B -
There was also a T-412/ART-13B that added a 4 channel LF/MF and 20
channel HF crystal oscillator module, the CDA-T in place of the LFO
module. The CDA-T was built by Communications Company, Inc.(aka COMCO,) who generally supplied
the module with a full installation kit that included extensive
instructions and directions for the conversion of either the ATC, the
T-47/ART-13 or the ART-13A. When the CDA-T was installed and the
transmitter fully converted to the "B" version then, with the selection of each of the
transmitter channels 1 to 10, two
different crystals could be selected giving the user two frequencies per channel
or a total of 20 HF channels in all. Also with the CDA-T installation a
"frequency extension" modification was added that changed the lower end of
the frequency coverage down to 1670kc. The LF position allowed the
selection of four crystal controlled frequencies on the CDA-T
module. The remote used with the "B" version will have a toggle switch
to allow selecting either crystal frequency per channel selected.
"B" versions of the ART-13 are conversions of earlier
ART-13 or ATC transmitters. Be aware that you can't just install the
COMCO module and have your ART-13 become a "B version. In fact, the CDA-T
can't even plug-in. The installation of the "B" version CDA-T
module required extensive modification of the transmitter
circuitry along with the addition of a second Jones Plug for the module
and an additional wafer for the REMOTE-LOCAL switch along with
several additional components (supplied in the kit with the module.)
Most ART-13B conversions that were performed by the military during WWII
will have riveted tags installed to identify the frequency extension
toggle switch and another tag riveted over the original transmitter data
plate that identifies the conversion to T-412/ART-13B. Post-WWII
conversions generally don't have these riveted tags installed. Since
there was no modification to the Autotune of the ART-13 transmitter, each of the A/B crystal
channels had to be set very close in frequency to each other, otherwise
the transmitter wouldn't be tuned for one or the other of the lettered
photo left: The Crystal Oscillator Unit for the ART-13B. Built by Communications Company, Inc. (COMCO.)
- The T-47/ART-13 had a very long life. Introduced around 1942,
actively used during and after WWII and well into the sixties. The
Grumman HU-16 air-sea rescue amphibians were equipped with
ART-13/BC-348s until the late 1960s. The
USSR also produced a copy of the ART-13 that they used up to the late
1980s (the R-807.)Because of its long useful life, most T-47/ART-13
transmitters found today will have many scratches and a few dents
and paint scrapes. Sometimes non-matching modules will be encountered
with some parts having MFP applied and others that are bare. A book
containing brief instructions and the calibration settings for specific
frequencies is usually stored in the metal pocket underneath the
transmitter. Earlier versions of the transmitter will have a somewhat
thinner (and always missing) book not "chained" to the pocket.
This earlier book is specifically for the two tube version of the MCW/FCI
module used in the ATC and early T-47 transmitters. Later
versions have a thicker book that is specific for the three tube version
of the MCW/FCI module used in late T-47 and all ART-13A versions. The
later book has a plastic tubing covered chain
that was supposed to keep the book "tied" to the transmitter. This
later book is also usually missing on most transmitters (although the same
information is in the standard manuals.) Luckily,
thousands and thousands of T-47/ART-13 were built and spare parts are
very easy to find which allows for the fairly easy restoration and
maintenance of these durable and potent transmitters.
photo right: The Collins ATC chassis showing some of the differences between this very early version and the later ART-13. Notice the earlier, two tube version of the MCW/FCI module (the large cylinder upper right is the crystal) and the absence of the large LF relay K-105. Also note the Collins tag on the modulation transformer.
Selecting an ART-13 Candidate for Restoration
Assessing your potential restoration candidate prior to purchase is important for a successful completion of the project. Choosing the right ART-13 is certainly going to determine how long it takes you to complete the project and get it "on the air." There are a couple of tests that should be made if you have access to the transmitter before purchasing. Also, some things to look for when buying on line.
|Technical Difficulty of Restoring an ART-13 - The ART-13 is a robustly-built but light-weight, compact transmitter. Since it is fairly small most of the components are installed into tight quarters and accessing most of the transmitter circuitry will require some disassembly. Fortunately, most of the transmitter design and construction allows easy disassembly to access and work on various parts of the circuitry. If you have serious problems in the Autotune section, this is difficult to disassemble and some of the parts are somewhat delicate. Same goes for the VFO-Multiplier sections which are difficult to access and the Multiplier uses very delicate stacked trimmer capacitors. Though the Audio and MCW/FCI modules are easy to remove, the components are densely mounted under the chassis. Most ART-13s will have MFP applied and this will compound the difficulty of any soldering work that might be required. Certainly an AC power supply (if opt'd for) will be the most time consuming to design and build. >>>||>>> You should have the following skills when taking on an ART-13 project. You should have some experience working on tube-type transmitters and working around high voltages. You should be experienced in full disassembly and reassembly of electronic equipment. If you decide on an AC power supply, you should possess "homebrewing" skills, that is, sheet metal working, component layout, proper wiring dress, etc. You should have good technician skills, possess a good soldering technique and use real SnPb solder with first class soldering equipment. You will need good quality test equipment. You will need a set of spline wrenches (also called Bristol wrenches) for all set screw applications. An oscilloscope is essential during testing and set up of the transmitter. You should possess good troubleshooting skills. Most hams that have worked on several tube-type transmitters and have built some radio equipment will have the necessary skills to complete the restoration of an ART-13.|
Candidate for Restoration - There are a lot of ART-13
transmitters for sale at swap meets, on eBay, from Fair Radio
Sales or from various online sources. ART-13s are not hard to find. But,
what is hard to find is a good condition, all original and complete
ART-13. Most of the transmitters that are for sale look like the one in
the photo to the right. Not a good candidate unless you are experienced
and looking for
a real challenge*. This candidate's condition is obvious but many times
the ART-13 you are looking at can have serious problems that aren't
obvious at all. A thorough inspection followed by actually testing a
couple of the components can help "weed out" a transmitter that is going
to need a lot of repair and restoration work.
A good candidate should be fully assembled and have all of
its modules installed. A few missing tubes are okay since they are easy to
find and not terribly expensive. Be aware though, missing tubes should be taken
as an indicator that the transmitter was considered a "parts source" at
one time and
may actually have some operational problems - not always - but
definitely investigate further if all
of the tubes are missing. Meters should be in good condition and they
are easy to test while in the transmitter. The meters are not difficult
to locate but the same caveat as with missing tubes should be
considered. Generally, a complete and good condition transmitter means
it has always been stored correctly, has not been abused and probably
has a pretty good chance that nothing serious will be found wrong in the
circuit or with the components. Be skeptical though! Even though the
transmitter might look great, it could have a serious, difficult to
solve problem that kept the transmitter from ever being used, thus it's
excellent appearance. Definitely, any transmitter that is missing parts should be
considered a "restoration project" that is going to require time
searching for parts and will need more time to get the fully operational.
photo right: T-47A/ART-13 "parts set." Note, even the multimeter glass is broken. Although restorable, this one would be a definite challenge.
Inspecting the ART-13 Before Purchase
|Thorough Inspection of the Transmitter - If you have access to the transmitter prior to purchase you can look it over in detail. The two "easy to remove" modules should be present. The three-tube MCW/FCI module is easy to find if it's missing but the Audio module is more expensive and a little more difficult to locate. Check the interlock switch on the T-47A/ART-13 versions since if the transmitter is placed upside down with the lid off (for quick and careless repair work) more than likely the switch will be broken. Check the wiring for anything cut or missing. >>>||>>> Check for broken parts. The Antenna vacuum switch is sometimes broken since it is a glass unit.Undo the locking bars and see if the controls rotate easily. Check the condition of the push connectors on the left side of the transmitter and make sure they aren't corroded and stuck. Also, check the condition of the U/7 connector and make sure the pins aren't bent or corroded. That's about all you can check visually. If the seller is agreeable, check the Modulation Transformer and the Meters as described in the following sections.|
|Testing the Modulation
Transformer - This is probably the most important part of
the transmitter that is sometimes missing and other times
non-functional. Finding a good condition replacement (if you need one)
is difficult and somewhat expensive. You will want to know "up front" if
the ART-13 you're contemplating buying has a non-operational
modulation transformer as this will seriously affect its selling price. You'll need to have a DMM
(Digital Multimeter) to check the modulation
transformer. You will be measuring the DC resistance (DCR) of the
windings. This test is not a 100% indication that the modulation
transformer is perfect but it's a pretty good test. Also, if the DCR of
a tested winding reads open, you then know 100% for sure that the
mod transformer is bad. Take care to make good contact to the terminals
with your test probes, especially if the mod transformer is coated with MFP. Note that each of the seven terminals are numbered. The three
terminals on the left side (assuming you're in front of the transmitter)
are from left to right looking at this side 6, 7 and 2. On the right
side the four terminals are left to right 1 and 3 on top and 4 and 5
on the bottom.
Be aware that the 813 screen windings have a different DC resistance on early units. The change occurred about the middle of the ART-13A contracts. It looks like the wire used for the the screen winding was increased in diameter for better durability which would then have the same turns ratio but a lower DCR. It's also possible that many of the earlier Mod transformers were noisy. My T-47/ART-13 has the earlier Mod transformer and it is very noisy when at full modulation. My AN/ART-13A however, has the later Mod transformer and it is quiet regardless of the modulation level. I have to test more ART-13 transmitters to confirm that this is a characteristic difference between the two types of Mod transformers. >>>
|>>> Here is the DCR between the various terminals with the Modulation
Transformer installed in the transmitter (with power off, of course.)
Terminal 2 to Terminal 3 = 136 ohms DCR
Terminal 2 to Terminal 1 = 123 ohms DCR
This test measures the DCR of the P-P 811
modulator plate winding. Terminal 2 is the CT of the winding.
Terminal 7 to Terminal 6 on early mod xmfrs = 150 ohms DCR
Terminal 7 to Terminal 6 on later mod xmfrs = 38 ohms DCR
This test measures the DCR of the 813 screen winding
Terminal 4 to Terminal 5 = 112 ohms DCR
This test measures the DCR of the
813 plate winding
If the transformer measures close to these DCRs, it is likely in good condition and useable.
NOTE: If you want to check the windings to chassis for case shorts be sure to place the CAL/TUNE/OPERATE switch in OPERATE. If you have that switch in the TUNE position, you'll have a 25K short to chassis on the 813 screen windings.
|Testing the Antenna Current Meter - This is an AC current meter that is driven with an adjustable core, single-turn transformer. The meter is .250mA FS and should to be checked with an AC source, such as a Function Generator. The Function Generator will have a very low output Z - probably 50 ohms. The polarity to the meter doesn't matter but you will have to disconnect it from T-102, the Antenna Current Transformer. Set the function generator frequency to anything higher than 100kc - it's not critical. It takes a pretty high level sine wave signal to move the Antenna Current meter needle but 15 volts Pk-Pk should read 2.0 Amps on a working meter. If a Function Generator is not available, a Digital Multimeter (DMM) will indicate around 3.0 ohms DCR across the terminals in both directions (due to the internal dual thermocouple) but the meter needle should not move with DC applied (from the DMM measuring DCR.) Again, you'll have to disconnect the meter for testing by either method. Generally, these meters were pretty reliable and are seldom non-functional.||Testing the Multimeter - This meter is a 1mA FS DC meter. Measure the DCR across the terminals and you should read about 40 ohms DCR. NOTE: Be sure to only use a Digital Multimeter (DMM) for this measurement. Older style VOM meters can apply enough voltage in some of the ohm scaling to do possible damage to the ART-13's multimeter. With a DMM, you will see some deflection of the meter needle. Be sure to observe the correct polarity. You are only checking the meter's continuity with this test, not its accuracy. To check the accuracy you would need a small DC voltage source that is adjustable and a 300 to 1000 ohm load resistor. Use the DMM set on DC mA with the FS at no higher than 10mA. Use the load resistor to limit the DC voltage source and connect the meter, the load resistor and the DDM in series with the DC voltage source. Adjust the DC voltage for a FS meter reading and then look at the DDM. It will read how much current is necessary to drive the meter FS. It should be very close to 1.0mA||Toilet Seat Covers - These are the protective covers that are usually on the KEY, both SIDE TONE and the MICROPHONE jacks. The T.S., or Throttle Switch (remote PTT,) jack doesn't have a protective cover. These are mentioned here because some ART-13 variations will be found without the Toilet Seats installed. This is correct for certain sub-model variations. All ATC versions don't have toilet seats. NT-52286 is another variation that did not have the protective covers and there may be others. Check the panel carefully for originality if the Toilet Seats are missing. Original installations use rivets to mount the covers so any removal operation would be obvious.|
|Buying an ART-13 Online - If the only source available to you is eBay or QTH.com or some of the other online venues, your inspection is going to be cursory, at best. Photos only show so much and detail is often lacking. Most of the time the seller doesn't show what is important and has several irrelevant photos. You should ask questions or ask for more photos. Generally, if the transmitter appears to be in great condition, then it probably is complete and was stored carefully. You won't know the condition of the components unless the seller has taken the time to test them and will guarantee their condition. Buying online, especially on eBay, will result in paying the highest price, plus paying for shipping (where damage may also occur.) Since you will be paying "top dollar," you should be assured that the transmitter is in good condition and will be packed carefully for shipping.||
Modified ART-13 Transmitters -
The ART-13 was the subject of many modifications generated by the CQ
magazine crowd. CQ published "The Surplus Conversion
Handbook" which contains two or three articles on ART-13 "modification
for ham use." Although we cringe today at such "hacking," it was
commonly done in the fifties and sixties. Consequently, finding an
ART-13 in modified condition is fairly common. Some of the mods were
intended to increase the transmitter's frequency coverage. There were
mods to extend the lower end to cover 160M, although many ART-13s will
tune about 25kc into the top of the 160M band without any modification.
There were other mods to extend the upper end to 10M. The 10M mod pretty much did extensive damage that is
difficult to restore to original. Also it's very common to find some of
the Antenna/Condenser/Loading Coil/Ground push connectors replaced with
SO-239 UHF coax receptacles. Again, damage to the connector panel is usually
Try to stay away from modified ART-13 transmitters. There are a several minor upgrades or modifications out there that have some benefit and enhance the performance but generally the ART-13 can be operated in its original configuration without any problems.
Since so many of the manuals are available on-line, it's probably a good
idea to download them and become familiar with the transmitter before
you actually purchase one. That way you'll know what to look for and how
to describe certain parts of the transmitter that are somewhat unique.
T.O. 12R2-ART13-2 is the Maintenance Handbook for the ART-13A and is a very good source of information. Available on BAMA (Boatanchor Manual Archive)
NAVWEPS 16-30ART13-5 is the Maintenance Handbook for the ART-13. Available on BAMA
Several other manuals were published over the years. Some are available on-line but the majority of these lesser known manuals have to be purchased from other sources.
Deciding How to Power the ART-13
By now you should be considering how you are going to power up your ART-13 when you finish the restoration. I'm not trying to talk the potential ART-13 operator out of using a Battery/Dynamotor set-up but there are several "pit-falls" that will come up when attempting this method of operation. Building an AC operated power supply is the most common approach but it usually is the most time consuming part of the entire restoration project. The following information comparison may help you come to a decision.
Using the Original Battery-Dynamotor Set-up
|If you decide to go original
and use one of the dynamotor-battery combinations, here's some things to
1. The DY-11 and DY-12 are difficult to find and usually are in original condition which means they may require some rebuilding to function well. The DY-17 is the more common version but it is still very difficult to locate. Since most casual ART-13 "parts collector-dealers" think the DY-17 is the only proper dynamotor, it is usually the most expensive one to purchase, if it can be found. Same holds true for the later DY-17A. All four types of dynamotors work with the ART-13 but all four are difficult to find and, when found, will be very expensive. Another word of caution on dynamotors in general,...many of the units found will have problems that cannot easily be repaired. A shorted armature might require rewinding and, if you can find anyone to do it, the costs will be staggering. A recent quote to rewind a DY-17A armature was $3300 from a rebuilder in Los Angeles! If you want to go the dynamotor route, try to arrange a test of the unit prior to purchase to see if it will operate correctly when powering an ART-13. Even with a shorted armature, the dynamotor may rotate and seem to work. You must test it actually powering up an ART-13 before you know it's usable.
2. Using two 12vdc deep-cycle marine batteries connected in series to provide +24vdc for dynamotor/xmtr power is not recommended. The batteries will have to be kept charged in some manner. Charging lead-acid batteries in the house or ham shack can be dangerous and certainly is smelly. Additionally, the batteries alone will only provide about +25vdc after charging and the voltage will drop rapidly as the transmitter/dynamotor are in operation. In the airplane, the transmitter/dynamotor ran on a battery-charger system that provided an almost constant +28vdc while the airplane was aloft. This is where the ART-13 runs best. Typical power output using the dynamotor on just batteries will be around 60W to 70W. With a charging system (+28vdc) power output will be around 100W. This is due to the speed that the dynamotor turns. The +28vdc turns the dynamotor at its rated RPM where it delivers the rated voltages. At lower battery voltages, the dynamotor speed drops and so does the voltage along with the transmitter power output.
3. To eliminate the batteries and run the dynamotor on a high-current +28vdc power supply is problematic due to the horrendous starting current required to operate the dynamotor. Although when turning at full speed (and powering the transmitter) the dynamotor load and the transmitter load requires nearly 40 amps, the initial starting current required by the motor section of the dynamotor is close to 100 amps. Although this starting current is very high it only lasts for a few milliseconds, that is, until the armature begins to move at which time the current demand drops rapidly as the motor armature comes up to speed. Even though the high current demand is for a very short duration, most modern, high current DC power supplies with current fold-back circuitry or other types of protection circuits will "see" the dynamotor as a "short circuit" and prevent the power supply from operating. The exceptions are some of the earlier military heavy-duty AC power supplies. These early style "linear" supplies can handle the surge of current demand since it only lasts for a few milliseconds. The GRC-106 power supply is rated at +28vdc at 50Amps and, if one can be located separated from the transceiver, it will operate the DY-17 dynamotor. Also, the heavy-duty "battery charger" unit, the PP-1104, can be used to supply +28vdc at well over 50A. These types of heavy-duty power supplies can provide enough current to start a DY-17 dynamotor. Also, there are portable airport-type power supplies used for starting airplane engines. These are available up to 200 amps at +28vdc. However, "expensive" is an understatement. More details on the PP-1104 below.
4. Another solution is to run the lead-acid batteries with an adjustable 0 to +50vdc power supply capable of providing at least 40-50 amps. That way, you can adjust the power supply to have the battery system at +28vdc and simulate a charging system. The batteries will provide the 90 to 100 amps necessary for the initial starting current of the dynamotor. In essence, this combination simulates how the ART-13 operated while on the aircraft aloft. However, the hassle of running both batteries and a high current power supply seems to complicate a problem that can be easily solved by using either the PP-1104 or GRC-106 PS.
|Using the PP-1104 to
power the ART-13 & Dynamotor - Details - The PP-1104
was originally supplied to the military as part of a battery
charging system. To say that the power supply is robust is an
understatement. It is capable of supplying well over 50 Amps at
28vdc and has the ability to adjust the output voltage to compensate
for the load. There are two versions of the PP-1104, the early
version that uses a large selenium rectifier and the later version
that uses silicon diodes. Both have similar performance
specifications. Early versions are designated as PP-1104-A/B and
later versions are designated as PP-1104-C. Many different
contractors have built these power supplies over many years so there
are variations galore as to minor construction details and paint
colors, etc., but the specifications and performance are all the
same. The physical size of the PP-1104 is about 24" tall by about
20" wide by about 12" deep. The weight is over 100 lbs for the early
versions and just at 100 lbs for the later versions. The power
requirements are either 115vac or 230vac with the current draw at
between 10 amps to 24 amps depending on the ac voltage used and the
load. The power supply can also be set up for 12vdc at over 100amps
capability. The circuit uses two 12vdc solid-state linear power
supplies that can be connected in parallel or in series via front
panel links. Meters provide constant monitoring of output voltage
and current. A front panel switch allows for setting the output
voltage in roughly 10 steps. Output voltage should not be
adjusted with the unit turned on however. Set with power off and
then check with power on. The circuit on the later PP-1104 supplies
uses a magnetic amplifier to increase the current capabilities.
Also, a very small internal power supply feeds into the main supply
to provide voltage regulation.
Curing RFI in the PP-1104 - Some PP-1104-C versions are rather noisy in the RF spectrum and the magnetic amplifier will produce some RFI. These units can be set-up with shielded AC lines coming in and shielded cables for the output. Be sure that the case of the power supply is also connected directly to the station ground system with a 10 ga. ground wire. Additionally, it's a good idea to bypass the AC line in with .01uf capacitors to chassis and to also bypass both the positive and negative output terminals with a .22uf tubular and a .01uf ceramic disk capacitors connected to chassis. Be sure to check the 10-32 screws that mount the top cover, the bottom and the back cover to see if good grounding contact is being achieved. Usually the paint is very heavily applied and quite hard which insulates the covers from making good contact to the main frame. It's usually necessary to use a small sanding disk to remove the paint where each screw head makes contact and remount the screws using toothed lock washers. This will provide an "RF tight" enclosure which helps considerably in reducing RF noise. Thanks to Jerry W6JRY for the PP-1104 RFI suggestions.
Operation - Using the PP-1104 to operate dynamotors eliminates most of the headaches since the power supply is capable of providing the starting current without hesitation. Also, since the PP-1104-C can be adjusted to over 40vdc output voltage, adjusting to 28vdc under load is easy and allows the ART-13-dynamotor combo to run efficiently and with maximum RF output power (100 to 110 watts typically.) You might find that the unloaded voltage (when you're not transmitting) might be a little high running up to maybe 30vdc but it is possible to adjust the PP-1104 to find the best compromise of loaded versus unloaded conditions. Also, you can use a large variac on the AC input of the PP-1104-C to have a fine adjustment of the output voltage dependent on the load. Be sure the variac is at least 18 amps or larger (assuming 115vac nominal input voltage.) Usually, though, a good compromise is easy to find that provides maximum voltage under load versus minimum "voltage soar" when unloaded. Typical excursions are around 2vdc to 3vdc. So, assuming a minimum change would allow 27vdc under load and 29vdc in the unloaded condition, which would be ideal. Remember that the ART-13 tube filaments are running on the PP-1104 in both transmit and receive, so try to keep the supply voltage as close to 28vdc nominal as possible.
Basic Design Requirements for a Homebrew AC Operated Power Supply
General Information -
Due to the difficulties involved in
battery-dynamotor operation, most ART-13 users opt to build an AC
operated power supply that provides +1150vdc, +400vdc and +28vdc @ 10
amps. There are several schematics available on the web and in various
magazine articles, even in old surplus conversion handbooks. How
elaborate the supply is depends on the desires and abilities of the
builder. It is possible to connect a +750vdc
power supply in series with the +400vdc power supply to create the
+1150vdc. That's the way the +1150vdc was achieved in the dynamotors and
it's perfectly okay to simulate this approach in an AC power supply. The
advantage is the power transformers are much easier to find as are most
of the other components necessary for that approach to the supply.
Many users want to increase the HV to have higher power output from the ART-13. Most ART-13 users feel it's safe to increase the HV to +1500vdc. At this level your power output can be around 175 watts. Some users run higher voltage without any problems. +1800vdc will result in about 200 watts output. Above this level though some audio distortion might be experienced. In fact, there have been reports that the screen tap on the modulation transformer may be responsible for slight audio distortion above +1300vdc +HV, though this is not typical. The 813 is rated for around +2200vdc and the 811s somewhat higher. Generally, if higher plate voltage is desired then separate +HV and +LV power supplies are used.
If plate voltages higher than +1150vdc are used, be aware that you probably won't be able to use the recommended military carbon microphones and achieve full modulation. This is primarily due to the fixed gain of the audio module. Even though the plate voltage of the modulator tubes is at a higher level, the +LV voltage isn't and therefore not enough audio drive is available using stock military microphones. It is possible to increase the +LV about 10%, or up to around +440vdc and this will provide better audio response (in addition to some help in the grid drive to the PA.) Don't increase the +LV any higher than +450vdc. Use of an externally amplified microphone is usually necessary when running the ART-13 at higher plate voltages. However, this is very easy to accomplish using an Astatic TUG-8 amplified microphone stand. >>>
>>> The Plate Current meter operated with a 13.4 ohm WW and a 6.7 ohm WW resistive bridge that was installed in the dynamotor. Total Plate Current for the 813 and the two 811 tubes is being measured by routing the -HV through the shunts and the meter. Most AC power supply designs use separate +HV and +LV supplies which can then utilize a single 20 ohm WW shunt with the shunt connected to U/7 pin 2 (-HV) and to U/7 pin 9 (Meter positive) with pin 9 connected to Chassis. The Plate Current meter will read 200mA FS using a 20 ohm shunt. When increasing the +HV higher than about +1250vdc, it will be necessary to recalibrate the Plate Current meter for higher full scale capability. This is usually accomplished in the AC power supply design by using an adjustable Ohmite resistor to replace the fixed shunt.
The original bridge resistor in the dynamotor was a tapped 10W WW resistor but most AC Power Supply designs using separate +HV and +LV use a higher rated adjustable shunt resistor for increased reliability and protection of the Plate Current Meter. Most users adjust the value to have the Plate Current read 2X of the meter scale. The Grid Current and Battery Voltage functions are not affected by this resistor change - only the Plate Current. If series +HV and +LV supplies are utilized then two resistors should be used. From Pin 2 (-HV) to Pin 1 (+LV) a 13.4 ohm series load is used and from Pin 9 (Meter +) to Pin 1 (+LV) a 6.7 ohm series load is used. Pin 9 is not grounded or connected to chassis in this configuration. This hook-up duplicates what is found in the dynamotor.
How to provide the +28vdc at 10 amps is very easily accomplished by using modern, small, solid-state switching power supplies. These can be often found with current rating higher than 10 amps which will assure that you have sufficient current to operate the Autotune on the ART-13. Remember, in addition to the ART-13 tube filaments, relays and the Autotune motor, you are also going to be operating the two relays in the AC power supply with the +28vdc power supply section so extra current carrying capability is desirable. Anything 10 amps or higher will work fine. Another thing to remember is that modern switching power supplies are not like the ones designed and built two or three decades ago. Older "switchers" had excessive noise on the outputs while the modern (designed in the past several years) are noise-free and quiet in operation. Try to find a modern "switcher" and you won't have any problems. One more note, most +24vdc "switchers" will adjust up to +27 to +28vdc with no problem, so you don't have to look for a "28vdc" power supply. 24vdc "switchers" are easy to find and will adjust up just fine.
|The Vacuum Tube Rectifier
It is up to the builder of the AC power supply to decide if they want to
use vacuum tube rectifiers or to go solid state on the +LV and +HV. When
opting for vacuum tubes remember, you will have to provide filament
voltage for the rectifiers and, due to the nature of the ART-13's PTT
system, this will require using separate filament transformers. You'll
also have to provide tube sockets and the necessary sheet metal work to
mount these pieces.
If mercury vapor (MV) rectifiers are used in the +HV, you could experience "flash-over" at sometime - always exciting! 866A MV tubes can be replaced with the 3B28 High Vacuum Rectifier tubes to avoid future problems. For the +400vdc, you'll have to use a 5U4GB and be sure it is the "GB" version since only that type has the current carrying specs necessary. You could use two 5R4G tubes for sufficient current capabilities but this will require one more socket, more sheet metal work, in addition to the increased filament current requirements. The 5U4GB will handle the current and voltage with just one tube.
Though vacuum tube rectifiers are cool, going Solid State is much easier. No sockets, no filament transformers, no sheet metal work, etc. For the +HV, you can use replacement microwave oven diodes (NTE 517) that are rated at 15KV PIV. These diodes seem to work quite well in the +HV application. Reference the section below "Homebrewing an AC Operated Power Supply for the ART-13" for detailed information including schematics of both Solid State and Vacuum Tube Rectifier type supplies.
Construction Details - ART-13 Power Supplies will have at least two large transformers for generating the +LV and +HV. Transformers will have a electromagnetic field surrounding them while in operation that varies the flux at 60Hz. Most transformers are shielded but some of the field is still present on frame type units. Potted transformers are the best of the shielded designs. Most power supply layouts will first separate the two supplies, the +LV and +HV, at opposite ends of the chassis. Orientation of the cores at opposite angles will also help reduce magnetic coupling. Use of a steel chassis will help to separate the control circuits from fields. Finally, a steel cabinet that is grounded to the chassis and to the ART-13 will help to reduce coupling problems. Note that since the ART-13 cabinet is entirely made out of aluminum, it offers little protection against low frequency magnetic coupling problems even though it is grounded. If an ART-13 AC power supply has no cabinet or an aluminum cabinet and it is placed close up next to the right side of the ART-13, the power transformers of the power supply are very close to the Audio Module with no protection against magnetic coupling. Likely some 60Hz hum will appear on the audio of the transmitter. An easy solution is to locate the power supply further away from the ART-13. However, if a steel cabinet is used in construction the magnetic coupling is shielded and the ART-13 can even be placed on top of the power supply with no magnetic coupling issues.
ART-13 Power Cable Construction - In addition to the power supply, a power cable will have to be built. At least one U/7 plug will be needed. The cable should have two 14 gauge wires and eight 22 gauge wires. I use 6000vdc rated test lead cable for the one +HV wire since physically it's not any larger than the 14 gauge wires. Perhaps unnecessary but it gives some added protection at +1500vdc or more. The cable should be wrapped with electrician's tape to keep the wires in place and then the entire cable should have a braided shield installed over it. This shield is important because it not only keeps RF out of the cable but also provides the chassis to chassis connection from the ART-13 to the AC power supply. This helps to distribute the ground returns and simulates the ART-13 to aircraft frame connections of the original installations. To make the shield I use a length of RG-8U coaxial cable and remove the outer jacket. Then push the shield together a little bit and the center conductor and dielectric can easily be removed. Then slide the shield over the ART-13 power cable and pull the braid tight. Finish by wrapping the shield with two layers of electrician's tape. The shield should be connected to the ground pins on each end of the cable. Usually about 60 inches is a good length for the cable. Longer cables will have more of a voltage drop on the high current wires. The cable can connect to a terminal strip on the power supply side to avoid having to buy two U/7 connectors and a U/7 box. These connectors sell for about $60 each. >>>
Here are the connections to the 10 pins of the U/7 connector,...
Pin 1 = +LV, approximately +400vdc
Pin 2 = -HV, this is the minus return and is provided for the total Plate Current shunt function connected to the minus (-) of the Plate Current meter via the selector switch. If series +HV and +LV supplies are used then Pin 2 connects to Pin 1 (+LV) through a 13.4 ohm WW resistor. If separate +HV and +LV supplies are used then the -HV (pin 2) is connected to chassis through a 20 ohm WW shunt.
Pin 3 = +PTT line, this is approximately +28vdc with the PTT function actuated
Pin 4 and Pin 6 = +28vdc input (use separate wires to distribute the current load.) Generally, pin 6 provides voltage to the tube filaments and pin 4 provides voltage for the relays and Autotune.
Pin 5 = Chassis, Ground - Use
a separate ground connection to the ART-13 case
to help distribute the current load. The power cable shield should
provide an excellent chassis to chassis connection between the
transmitter and the power supply. This will help simulate the
chassis-case connection to the aircraft frame that was part of the
mounting system. It is also advisable to connect the ART-13 to the
station ground by a wire connected to one of the case screws.
Pin 8 = -PTT line, this is the chassis connection with the PTT function actuated
Pin 9 = Positive (+) connection to Plate Current meter via the selector switch. This can be connected to Pin 5 or chassis if separate +HV and +LV power supplies are used along with a single 20 ohm shunt. If a series +HV and +LV are used (simulates dynamotor connections) then Pin 9 is connected to pin 1 (+LV) through a series resistor of approximately 6.7 ohms.
Pin 10 = +HV, high voltage for 813 and 811 plates (use HV test lead wire or similar)
Restoration Hints and Suggestions
The Mechanical Stuff
Mechanism - The Autotune is made up of four 360º
rotation (single turn) modules and one 20 turn module. These modules are
driven by a Line Shaft that has worm gears on it that mesh with the
drive gears in the five
modules. The line shaft is driven by a reversible direction motor that
is controlled by a motor drive relay. Additionally, the Channel Selector
switch works in conjunction with the motor driven (from module A,) rotating Selector
Switch to determine which channel has been selected. Finally, there is a
Forward Limit Switch and a Rear Limit Switch that reverse the direction
of the motor and provide the stop function by removing a short circuit
condition on the motor current resistor (when the cycle is completed, a
small "locking" current flows through the motor windings.) The two limit switches that
basically control the cycle are located on the 20 turn module since its
operation requires the longest time to achieve its set point.
Important Note: Do not try to adjust the knobs of the Autotune section while the Locking Bars are tight. Anytime you want to adjust the settings of the individual control, first undo the Locking Bar and then make your adjustment. Then retighten the Locking Bar. If you make adjustments with the Locking Bar tight, you'll upset the presets for that channel and possibly all of the other channels too. You can also place the Channel Switch in MANUAL and let the Autotune cycle. Afterwards you can then manipulate all of the controls with the Locking Bars tight and you won't upset the presets.
As soon as you power-up the +28vdc line to the ART-13 the Autotune will begin to function if the Channel Selector switch position has changed since the last time the transmitter was in operation. The Autotune cycle first runs the five modules to a "zero" position and continues until the Forward Limit Switch is actuated which then reverses the motor direction. In this rotational direction each of the modules will lock in a preset condition determined by where the controls were "preset" for the particular channel selected. After all five controls have locked in position the motor continues to run until the Rear Limit Switch is actuated which stops the motor rotation by placing the current resistor in series with the motor windings. This method of stopping the motor was used to provide enough current to "lock" the motor in position, preventing the controls from being accidentally moved by vibration or other methods. The entire Autotune cycle usually takes about 25 seconds to complete. When completed the PTT line and the Keying relay operation are returned to functionability and the transmitter can be put into operation.
Quick Test - A quick test of the Autotune can be accomplished by just providing +28vdc at about 10 Amps (this is the filament load plus the Autotune load, which is about 1 Amp while running.) Connect the power supply to pins 4 and 6 for the positive and pin 5 for the negative. You should use at least 16 gauge wire, 14 gauge is better. Switch on the power supply and the Autotune should start its cycle. If it doesn't, change the channel. If everything is okay the cycle should complete in 25 seconds and the motor will stop. Change the channel and the cycle should start again and complete in 25 seconds. This quick test shows that most of the Autotune is working. It will probably need lubrication and preset adjustment.
Lubricating the Autotune Mechanism - The Line Shaft runs in bronze sleeve bearings and in ball bearings at each end. These bearings should be given a drop or two of light weight oil, 10W is good, something like sewing machine oil. Each module is driven by a worm gear that is installed on the Line Shaft. All of these worm gears should be coated lightly with light weight grease using a long handled paint brush. Each of the gears associated with each module can also be lightly coated in the same manner. Use a drop of machine oil on each of the bearings on the rotating gears. Use oil sparingly on the chain drive and don't stand in front of it during operation with the cover off after lubrication - you'll end up with oil all over the front of your shirt! (Yes, I've done it.)
Common Autotune Problems - Since the Autotune cycle controls the PTT line and the Keying relay operation, if there are problems with the Autotune, you won't be able to run the transmitter. Most of the time, the Autotune mechanisms are still in good condition because they were well protected by the front cover which even has felt seals around each opening to keep out dirt and dust.
If the ART-13 you are inspecting to purchase has been disassembled and the front Autotune cover removed or left off, be very wary of the transmitter. The Autotune is difficult to work on if complete disassembly is required. Look for a transmitter that is complete and shows no indications of having been a "parts set" at some time past.
That being said, the most common problems with the Autotune involve the limit switches. The Forward Limit switch is mounted on the extreme right side-front of the 20 turn module and can easily be hit or bent with careless handling of the transmitter with the front cover off. The Rear Limit switch is a "rocker" type switch that is very, very delicate and if damaged it is difficult to get it to work correctly again. Fortunately, it is further back in the module and a little better protected from damage.
If the Forward or Rear Limit switches aren't making good contact it will cause the Autotune to operate to "zero" position and then it will just set there with the motor continuing to run. With the Forward switch it is very simple to carefully bend the arm so that the rotating screw-driven actuator arm just opens the switch at the "limit position."
Opening the Forward Limit switch momentarily will reverse the motor relay position and reverse the direction of the motor so that the "preset" operation of the Autotune cycle can proceed. The Rear Limit switch has a spring-loaded contact that relies on a longer flex arm with a fiber button as the mechanical contact. Be careful if you have a mechanical problem with the Rear Limit switch. Very minor adjustments are all that should be required if it doesn't actuate. Bending of the arms should be avoided. Most problems with the Rear Limit switch are caused by contamination or dirt and not the mechanical adjustment of the switch arms.
Synchronization Problems - Sometimes the Autotune presets are not where some of the individual modules end up stopping. Most of the time this is dirt or contamination in the particular module's clutch. Try re-setting the preset and operating the Autotune cycle several times. Usually each time the module will stop closer and closer to the preset point. The operation seems to clean the clutch which results in accurate preset response. Sometimes the selector disks are not in the proper location to allow the pawl to drop into the slot and stop the control. Inspection of the module while in operation can confirm if this is what is happening. To correct, loosen the lock bar and rotate the particular selector disk to a position where the pawl can drop correctly, then tighten the locking bar.
Sometimes one or two modules will always operate to the end limit on a particular channel. Check the springs on the pawls to see if one of the springs has is not in its proper slot. Sometimes these springs become caught in the selector disks and will get bent. This is uncommon but it depends on how badly the particular ART-13 was treated in the past.
If you have an insolvable problem with one or more of the modules, they are easy to replace, but you'll have to re-synchronize the other modules to the new module. To remove a module first take the front cover off. Then remove the locking bar and the knob. Remove the knob backing plate and you now have access to the two slotted head screws that mount the upper part of the module. Remove these two screws and the lower Philipp's Head mounting screw. If you are removing the Antenna/Loading modules, you'll have to remove the screws that mount the phone jack bar to these modules. The bar only has to be dismounted and placed slightly out of the way to remove the module. The module engages the worm gear of the main shaft and has a spline drive socket at the rear that drives the particular control. Install the new module and replace the screws in reverse order.
Details on knob and module synchronization follow in the next section.
photo above: PA Tuning and Loading section of the Autotune. These modules are single turn, 360º rotation, driven by the line shaft. Between the two left-most modules is the motor drive relay. Note how the phone jack bar mounts to these three modules.
the Autotune Knobs - If you have to remove the five large
knobs you'll find that there is no obvious shaft flat or other indicator
of how the knob position relates to the shaft position. Fortunately, all
of the controls have mechanical stops at both ends of rotation. First
set all of the controls fully CCW (be sure to loosen the locking bars.) Set the knob positions as follows:
A - Rotate shaft fully CCW. Be sure that the small turns counter is at zero and at the mechanical stop. Then set the large knob to zero. Remember, all of the set screws require a Bristol wrench.
B - Set shaft fully CCW and set knob to slightly before the triangle #1
C - Set shaft fully CCW and set knob in the middle between triangle #1 and triangle #13
D - Set shaft fully CCW to stop and set knob in the middle of the non-scaled portion of the skirt (it will look like it's upside-down)
E - Set shaft fully CCW to stop and set to 0 on 100-0 scale
Tighten the locking bars and actuate an Autotune cycle. Since the knobs are already at zero, the knobs shouldn't turn until the forward cycle begins. Confirm that the controls stop correctly. Specifically, B should stop on a triangle, as should C. Also, confirm that D stops in the scaled portion of the knob.
|Synchronizing the Modules
- If you have to replace a module or if you've removed a module for some
reason, you'll now have to synchronize the newly installed module
to the rest of the Autotune modules. The procedure in the manual is
difficult to understand because it references all synchronization to the
A module since it isn't adjustable (because it drives the channel
selector switch.) Most of the time you're
going to have one of the single-turn modules that isn't in sync with the
other single-turn modules. To do the synchronizing, you'll need a way to
manually move the Line Shaft via the slotted and tapped hole (4-40) on
the right-hand side of the Line Shaft. Originally, the spare parts kit
contained a crank that was for that purpose but nowadays the cranks are
next to impossible to find. Some technicians use a screwdriver or a
blade bit installed in a power driver. If you choose this option, you'll
have to be very careful not to damage the slot in the Line Shaft.
It's fairly easy to use a power driver (like a Makita) with a blade bit to position the Line Shaft and not damage the slot in the end of the shaft. Just be careful and make sure that the bit fits tight in the slot. You're going to be rotating the Line Shaft in a counterclockwise rotation.
To synchronize any C, D or E module to the A and B modules just remember to consider that all four sync'd modules should be considered as a single module and it is going to be necessary to sync them with the remaining module (that is out of sync.)
You'll have to disable the out of sync module by loosening the cam drum collar set screws and sliding the collar down the shaft. This allows the selector clutch drum to move but not move the cam drum. See which channel the out of sync module is set to by observing the spring and pawl drop. Now rotate the Line Shaft in the counterclockwise direction noting that the springs and pawls all drop simultaneously on the "in sync" modules. When you are one channel before the channel desired stop using the power driver for rotation and switch over to a regular screwdriver. This is to allow the next sequence to proceed slow enough to control. As you approach the correct Line Shaft position, you'll see one spring-pawl slightly lift and then the next channel's spring-pawl drop into place. Stop rotating the Line Shaft at this position. Now check to make sure that the out of sync module is also in the proper channel with the pawl dropped into position. Slide the cam drum collar on the "formerly" out of sync module back up into position and rotate it with your fingers very slowly counterclockwise. You'll feel a point where there is some noticeable resistance to the rotation, which is the drive pin coming into position. Tighten the collar set screws at this point. You may be only able to tighten one of the set screws but this is sufficient until rotation of the Autotune brings the other set screw into position. Test the synchronization by rotating the Line Shaft counterclockwise with the power driver. Each spring-pawl should drop into position simultaneously. No more than a quarter of a turn of the shaft should be necessary for all of the spring-pawls to drop into position - usually it's much closer than that.
Now, do a channel-select Autotune cycle to test that all of the modules are synchronized. Set up the presets on channel one, then proceed to channel two and then check that if returned to channel one, all of the modules select the proper preset. You can now do all of the presets for all of the channels, that is, if your ART-13 is ready to go into operation.
This shows the A module which
drives the rotating Channel Selector switch located behind the module.
This switch rotates until it is in the same position as the front panel
Channel Selector switch.
Photo B: This is a close up of a single turn module showing the cam drum. This is where part of the pawl drops into when a channel is selected. Also, the front part of the pawl drops into the slot in the channel locking rings on the clutch drum which determines the preset.
Photo C: This close up shows the cam drum collar which must be loosened and dropped down the shaft to disable the drive on an individual module for synchronization. The collar has a stop inside that couples a drive pin from the gear above. The drive pin couples to the collar stop and then, since the collar is set screw coupled to the cam drum shaft, turns it.
Photo B (left)
Refurbishing the Cosmetics
the Knobs, Dials, Locking Bars and Stop Plates The five large knobs are bakelite
with a brass hub. The set screws require a Bristol wrench to loosen. These large knobs project out somewhat and therefore
many times they are found chipped. If the knob is chipped, an original must be
found to replace it. These large knobs sometimes are found with the
white fill paint partially missing and when cleaning is attempted, more
of the white fill paint falls off. These knobs are easy to recondition
by first removing them and then soaking them in a hot soapy water bath
for about one hour. Use a fairly stiff, brass bristle brush (toothbrush
size) and be sure that the brush bristles are very straight like a new
brush. Brush away towards the edge of the knob to clean the flutes.
Don't be real aggressive but go around the fluted section of the knob
twice with the brass brush to remove all of the finger grunge. Clean the
skirt of the knob with a regular toothbrush. You'll probably find that
most of the white fill paint will be removed in this cleaning. Dry the
knobs and they will be ready for a new fill paint.
Don't use "White" paint or lacquer-stik for the fill. This will be way, way too bright and will look terrible. Use Artist's Acrylic paint that is available from most Hobby or Art Stores. Mix white, light brown (raw sienna) and just a little black. You're trying to get a color that looks like a manila folder,...kind of beige. Though it looks too dark when you're mixing it, when you put it on a black bakelite knob, it will look aged white. Paint the entire skirt of the knob and give the paint about one minute to set. >>>
|>>> Next, use damped paper towel pieces that are about two inches square
and folded to wipe of the excess paint. Use Glass Plus to damped the
paper towel sections as this removes the paint much better than water.
Do a small section and then discard the towel - do not try to wipe more
of the paint with the same towel as you'll just spread the paint around
instead of removing it. Each wipe use a new damp paper towel. As you get
nearly all of the paint off, you'll notice the nomenclature looks really
great. Now, be careful and just use a very light touch to remove the
remaining paint. Normally, I have to do this application twice to get
the knob to look first-class and original. You don't have to wait to
apply the second fill. Once the knob is finished, set it aside and let
the fill paint dry overnight before reinstalling the knob.
The smaller switch knobs have an index line that has the white fill paint. Recondition these knobs using the same procedure as the larger knobs.
The locking bars and locking bar stop plates are often chipped and might have some corrosion. They are very easy to repaint. I first strip the old paint. You will then see all of the defects that were under the paint. Corrosion is common but can easily be removed with 400 grit aluminum oxide paper. Buff with 0000 steel wool. You don't need a primer but be sure to wash the pieces using lacquer thinner before painting. Mount the locking bars on a piece of cardboard so the paint won't get on the back of the bar or on the threaded shaft. I use nitrocellulose black lacquer and apply several coats to the locking bars. The stop plates only need a couple of coats. Let the paint dry overnight and then use lacquer rubbing compound to smooth the finish and then buff. The locking bars and stop plates will look original.
the Front Panel and Cabinet Paint - Since the front panel
nomenclature is silk-screened, a total repaint of the front panel
sections is not possible. Instead you'll have to use the "touch-up"
method. I use Artist's Acrylic "Mars Black" paint in a tube. This color
is very close to the original black wrinkle finish on the ART-13. If
dealing with the normal dings, flakes and scratches, the paint can be
used from the tube and applied with a Q-tip. Rolling the Q-tip will
impart a texture to the touch-up that looks close to the wrinkle finish.
This paint does dry flat with no gloss. On small areas this usually
isn't a problem.
For larger areas you'll have to use Krylon Black Wrinkle Finish (BWF) paint (or VHT Hi-Temp BWF brand available at O'Reilly stores) applied thickly with a brush. Spray some of the paint into a small cup and then use a brush to paint two fairly thick coats to the area. Let the paint set for a couple of minutes and then use a heat gun to "force" the wrinkle. Don't use too much heat or the paint will "gloss" and not match as well. >>>
|>>> Large areas such at the top lid can be conditioned by
using an Acrylic "wash." This is a very thin mix of Mars Black and
water. The mix should be about as thin as water but have some paint in
it. This mixture can be brushed on the top lid and the excess water
"dabbed off" with a cloth - don't use paper towels as they leave lint
and small pieces of paper towel behind in the paint. When dry the top
lid will look even with no chips or scratches showing. It will be "flat"
and not glossy but it will look better than a scratched up lid.
It is possible to use the Krylon BWF on many of the panels that comprise the cabinet but matching becomes a problem. Wherever there is silk-screening, the spray paint can't be used (except for touch-up.) Whether you can use the spray wrinkle finish to paint the lid or some of the panels will depend on the overall condition of the front panels. Be aware the painting the top lid is a very large area and very, very difficult to paint with wrinkle finish and not have "stripes" - areas that show the spray pattern. Try to spray at least four heavy coats with each coat applied at a different angles. This is the best way to avoid the "stripes." You'll also find that the Krylon BWF has a lot of gray in the mix and won't match the transmitter very well in certain light. VHT's BWF is closer to true black. After the new paint has set for about a week, you can apply a matching wash of Mars Black to get the top to more closely match the rest of the transmitter.
T-47A/ART-13 "Basket Case" Restoration
This example of the restoration process features a really awful condition T47A/ART-13 (aka: AN/ART-13A) that was part of a trade-deal. Missing parts, extensively disassembled and cosmetic condition issues make this an excellent example to illustrate the types of problems involved with the restoration of "Basket Case" projects - and, perhaps, why to avoid them.
|The Big Trade
- The photo to the right shows the USAAF T47A/ART-13 that I got in a trade.
The fact that it was almost completely disassembled didn't matter since it was
initially considered just a "parts set" to use for the restoration of another
nearly complete US Navy Collins T-47/ART-13 that was also included in the trade. I
know,...you want to know about the trade, right?
I got an e-mail offering two "rough" ART-13 transmitters, a "nice" BC-312 receiver and an "okay" BC-344 receiver plus several boxes of military radio parts in trade for audio gear or a tube tester. After a couple of e-mails we settled on trading a nice, working Hickok 600A tube tester and a "needs restoration" HP-713A power supply for a "load" of military gear that included the two transmitters and the two receivers. Photos were sent both ways and we both knew the condition of everything involved in the trade. A quick daytrip to Lafayette, California resulted in dropping off the tube tester and the HP power supply and coming back home with my Subaru Outback packed full of military equipment and parts.
First Things First - The first project was to restore and get operational the Navy T-47/ART-13. This project took a about seven weeks to complete, which included designing and building a suitable power supply for the transmitter. I began using this T-47ART-13 a lot and really enjoyed operating it. I didn't really consider even looking at the other ART-13 transmitter because it was a "basket case" and only a source of parts. Then, a few months later, fellow ART-13 enthusiast, W7MS, happened to mention "on the air" that he had a second ART-13 in storage that was his "hanger queen." This got me thinking that I probably could take my "parts set" and put it together enough to be a "hanger queen" that would be "for display only" in the museum. Functionability wasn't the goal, just a fairly complete, reasonably good-looking ART-13 for a museum display.
||The Parts Hunt
- As I searched for the parts I was finding boxes that had been picked
up at the Big Trade but that I hadn't really looked in carefully.
Looking through four large boxes turned up all of the sheet metal parts.
I looked through more of the smaller boxes and plastic bags finding nearly all of the
components that were missing. I began to think this project might
progress from "hanger queen" to "restore and get it operational." After a thorough search I ended up
with a pile of parts that looked like the photo to the left. In the
photo, all of the sheet metal parts were just setting in place, so I
could see that I had all of the pieces. Note that the combination bottom
cover and shock mount rails isn't even in place but is leaning up
against the side of the transmitter.
No amount of searching could find these missing parts: R-121, R123 and R-124. These are the wire wound resistors that are located in the rear compartment with the 811s and the 813. Additionally, the rear triangular bracket that supports the side panel for the blank panel couldn't be found. The MCW/FCI module and the Audio module "remains" had been sometime in the past totally disassembled for parts and I could only find the chassis and a few parts to those units. Also, the multimeter was unusable due to a broken glass that long ago had allowed the meter needle to become broken. Everything else that had been removed from the transmitter I was able to find in the various boxes of parts. This meant the transmitter was about 95% complete, just mostly disassembled.
In my "junk boxes" had two spare MCW/FCI modules so that wasn't a problem. KØDWC supplied the triangular bracket by giving me an entire blank panel assembly. I purchased an Audio module off of e-Bay. The meter and the wire wound resistors were obtained from Fair Radio Sales. So now, on to the restoration work.
|Unusual Reassembly -
The most difficult to repair damage was the three flexible plate cap
connections (E-109B) for the 837 VFO tube and the two 1625 multiplier
tubes. These consist of a flex connection and a brass tube that is
soldered to a stud that is mounted through a pair of ceramic standoffs
(top and underneath the chassis.) These three connections were "snapped"
off leaving the stud inside the brass tube and a flush threaded rod with a nut
on top of the insulator. After trying to drill out, tap and other
methods that didn't work, I decided that I should solder a flange to the
brass rod and then sweat-solder that to the nut on top of the insulator.
This worked quite well and seems pretty strong.
To reconnect the large buss wire connections for the LF relay (K-105) and the Antenna push connectors I made brass sleeves out of shim material. These cylindrical sleeves were fitted to the cut buss wires and then soldered. The buss wires had to be re-tinned first and it does take quite a bit of solder to fill this kind of splice. The benefit is that it's a really strong joint and it looks like a professional repair job. See photo right.
The Interlock switch had the housing broken. Fortunately, it was possible to use epoxy to repair the housing and get the switch working again. Also, the mounting for the plate blocking capacitor used a pair of fiber screws into the ceramic standoffs and since one of the fiber screws was broken, I repaired the mount using epoxy.
|A Wiring Error? - During the reassembly of the meter/switch panel I had to re-install the meter shunts and loads that are mounted with a long screw to a projecting tab that is on the back side of the right side inner panel. In checking the wire locations versus the schematic I discovered that the Meter switch had a wiring error. This was INCREDIBLE since it meant that the positions for Grid Current and Battery Voltage couldn't have worked. I used the wiring diagram (not the schematic) to confirm this was indeed an error. I think this must have been a later error done during a repair cycle that replaced the meter switch. It's likely that the transmitter didn't pass one of its tests after the rebuild and was set aside for a later checkout and repair cycle that was never done. The wiring error might have happened at SAAMA. The San Antonio Air Materiel Area (Kelly AFB,) performed extensive aircraft repair and repair of all aircraft equipment from 1947 up to 1974. This ART-13A has a SAAMA stamp for MFP application dated 15 Sept.1954. It's likely this ART-13 never made it out of the repair depot and was sold as surplus at some later date. The error was the interchange of two wires going to the Meter switch that introduced a conflict between the Grid Current and Battery Voltage. After switching the two wire positions, the meter then read Battery Voltage and Grid Current correctly. It's unlikely that this problem would have gone unnoticed, so why it wasn't corrected at SAAMA is a mystery. The photo left shows the SAAMA MFP stamp on the chassis.|
|Replica Calibration Book Pocket - The Calibration Book pocket was missing from this ART-13A. It appeared like the rivets were aggressively pulled out since the metal was slightly distorted. I took measurements from the USN T-47 that had its original book pocket and had a replica made at a local sheet metal shop. I had to add the curved cut-out and the edge treatment since this would have complicated the project for the metal shop. Once I had the piece shaped correctly, I had to remove the Autotune cover so I could accurately measure where the mounting holes had to be drilled. Also, there was some "body work" necessary to get the holes in the cover cleaned up. A close inspection of the original book pocket revealed that the inside was painted gloss black and the exterior was black wrinkle. The original wrinkle finish paint was a two part process that used a catalyst sprayed onto nitrocellulose lacquer to activate the wrinkle by baking in an oven. It's normal for older sheet metal pieces to be gloss on one side and wrinkle on the other. I painted the pocket with gloss black lacquer on the inside and Krylon Black Wrinkle Finish on the exterior. The original book pocket was mounted with round head rivets. Fortunately, I had the same kind of rivets in one of the parts drawers around here. The rivets are a tight fit and when the shaft part is deformed it pulls the mounting flange tight. The three photos below show the various stages of making the replica book pocket and the larger photo to the right shows the pocket mounted on the ART-13A. I still need to make the replica plastic tubing covered chain that attaches the book to the book pocket. A small hole at the lower right front corner of the pocket has a rivet/washer combination that holds the one end of the chain and a lanyard ring attaches the chain to the book binder ring. See updated photo at the end of this section showing the book, chain and ring installation.|
Cosmetics - As can be seen in the "before" photo above, the panels did have some aluminum corrosion that was "popping" through the paint. I used the method described in the restoration section above to touch up the panels. This ended up with a combination of touch up and then using the "wash" technique. This resulted in the panels looking kind of flat but even and with some wrinkle to the finish. See the "after" photos below.
Since so much of this ART-13A was disassembled and parts were obtained from other transmitters to complete its assembly, the distinctive "gold" color of the MFP coating had to be applied to many parts. Probably the most difficult to match was the replacement Audio Module since this was a large piece that didn't have any MFP coating when obtained. Fortunately, I had a few parts from the original Audio Module to see just how much MFP was on it.
Quite a few years ago, I had some yellow-tinted nitrocellulose lacquer mixed for me. This is very close to what MFP was except it doesn't contain a fungicide or that distinctive MFP odor (darn.) I thinned this yellow lacquer down using clear lacquer and lacquer thinner to get the correct "look" of the MFP when sprayed onto the Audio Module. >>>
>>> All of the other pieces that needed to be MFP coated were small - like screw heads and nuts, solder joints, sheet metal edges, etc. This was applied with a small paint brush direct from the tinted lacquer can. Looking at the finished chassis photo below shows the final appearance.
A new Settings Chart was necessary and an excellent one can be down loaded from BAMA. Just print it out on heavy manila paper and it will look original. New plastic for the chart can be found many places. I salvaged the plastic from a cheap picture frame.
Final Missing Parts Installation - The large wire-wound resistors, R-121, R-123 and R-124, were obtained from Fair Radio Sales. Luckily, when the originals were removed the wire must have been cut close to the resistor terminals because I did have enough wire left for the connections to the new replacement resistors. These large wire-wounds mount with an aluminum stud that is threaded on each end. The stud is mounted to the chassis with a screw and lock washer from underneath the chassis. Then several mica washers are placed over the stud and next to the chassis. Then the resistor is placed over the stud and secured with several more mica washers, a flat steel washer, a lock washer and finally a screw. Without R-121, you can't do any real "voltage on" testing because the +28vdc to the filaments is routed through this 0.8 ohm 50 watt resistor first. With the installation of these resistors the filament circuit is complete and testing can begin.
|Testing - I
tested both the MCW/FCI module and the Audio module by plugging them
into my working Navy T-47/ART-13 to confirm they were operational
units. The MCW/FCI module worked fine but the Audio module needed
extensive repair (what else can you expect from an eBay purchase?) Two
resistors had to be replaced. The audio input resistor had overheated
and the value changed along with burning off part of the color code
paint. The carbon mike Z load resistor had been changed from the
original value of 15K to 4.7K for some reason. I reinstalled a 15K
resistor. A quick operational check showed that I still had some
distortion that resulted in "harsh" sounding audio. The
problem was caused by a defective coupling capacitor between the 12SJ7
plate and the 6V6 grid (C-204.) Since this was one of a "stack" of three
molded capacitors (and one other capacitor already had broken mounting
tabs,) I went ahead and replaced all three caps with SBE Orange Drops.
Additionally, it was noted that the Jones plug was partially coming
apart due to a bent over tab not holding the back plate in place. After
several attempts to remount the back using the tab, I finally had to
resort to a combination of epoxy and the tab to hold the backing plate
in position. After these repairs, the Audio module output sounded great.
Pre-Testing - During the re-assembly of this ART-13A most of the sections that were affected by the disassembly were tested. A thorough inspection is necessary before powering up any transmitter. All components that could be tested with a DMM were given a cursory test. Be sure to test the Plate Blocking capacitor for shorts since this condition would allow for full +HV to be on the antenna system. All tubes are tested except for the 813 which can be given a quick filament continuity test and a quick shorts test with a DMM. Clean all the ceramic insulators.
Initially, I just connect +28vdc and make sure all of the low voltage circuits work. This test turned up a problem with the Autotune. Through the system would motor drive to the zero position it just remained at zero and would not continue onto the presets on any channel selected. Since the Autotune essentially wouldn't shut off, the transmitter couldn't be tested further until this problem was fixed.
Autotune Problem - I guess this transmitter was pretty much a basket case for quite sometime and the front cover was off of the Autotune mechanism. At that time the Forward Limit switch was hit or bent enough that it wouldn't open when the actuator arm contacted it. Momentary breaking of the contact would cause the Autotune to complete its cycle. I bent the contact arm just enough so that the contact would open at the Forward limit position and reverse the motor to complete the cycle. This got the Autotune working correctly.
+HV and +LV Test - When everything looked ready, I decided to go ahead with a full test. With the +28vdc on operation was normal and I allowed the tubes to warm up. After a few minutes, I switched to TUNE and pressed the THROTTLE SWITCH (T.S. jack - a remote PTT line.) This resulted in the immediate blowing of three fuses in my power supply. Two fuses were the primary fuses to the +HV and +LV transformers and one fuse was the +HV output. Since my power supply is fully fused in every input and output, no damage occurred there but certainly something was wrong the the ART-13A.
Problem One - The PTT line was grounded. This caused most of the problems involving the +400vdc. I traced the source of the problem to a solder bridge that I created when reinstalling K-104 - oops. Removal of the solder bridge cleared the PTT problem and the ART-13 would now operate and not blow the +400vdc fuse in the power supply.
Problem Two - The +1400vdc continued to blow both the transformer primary fuse and the output fuse in the power supply. A close inspection of the 813 tube socket revealed a burnt R-112, a 47 ohm 1 watt carbon resistor acting as a screen load. I replaced R-112 with an NOS resistor but wasn't too confident that it was causing the problem. I decided to also replace the old National Union 813 I had been using with an NOS Sylvania 813. These two changes got the +1400vdc and the transmitter operational and working fine.
|The Initial Shake Down
Test - This test used my homebrew power supply that I
normally use to power the Navy T-47/ART-13 to power this T-47A/ART-13
version. This supply provides about +1400vdc for the +HV and results in
about 160 watts output with the Navy transmitter. With the NOS Sylvania
813, this ART-13A had a somewhat higher output power running around 190
watts. I decided to use a variable capacitor (instead of a fixed value
capacitor) for the Auxiliary Condenser
so I could load the antenna exactly. This setup allowed me to adjust the
ART-13A for about 200mA total plate current and have a power output of about
145 watts. This allows the transmitter to run in a very stable manner
since the power supply current carrying capabilities are not "pushed"
and the +1400vdc plate voltage remains fairly constant during operation.
The reduced power also allows for easy 100% modulation without "loading
down" the plate supply (which was what was happening at 190 watts
output.) Monitoring with earphones listening on an RCA CR-88A (with no antenna
connected) sounded great. Watching the oscilloscope looked great. The next test was to
call up KØDWC and have him listen to the signal at his station (next
block up the street.) With this set-up, I
can also hear what Chuck hears via the telephone connection. Finally, a
true "On the Air" test with the Sunday morning Vintage Military Radio
net was next (3974KC - 8AM Pacific Time.) The "On the Air" test was successful and the reports that
came back were all positive.
photo left: The chassis of ART-13A sn 417ACG after restoration. Note the distinctive "gold" appearance from the MFP coating.
|CW Mode Inoperative
- This problem was actually found after I had used the ART-13A "on the
air" in the VOICE mode. I decided to try some 40M CW with the ART-13A
and after loading up in the VOICE mode, I switched to CW. When switching
to the CW mode, the transmitter should show plate idling current and when
depressing the key the plate current should increase up to slightly less
than the VOICE plate current (since you don't have the Modulator idling
current.) No idling current was showing on the meter and when the CW key
was depressed the keying relay operated but no plate current was
indicated. A quick check of the schematic showed that the problem was
most likely in the operation of the CW relay, K-103. A quick check
accessing the K-103 relay coil terminals for testing through the vent holes in the
rear panel of the transmitter showed the coil was open.
An original replacement K-103 would involve quite a bit of time to locate. Since rewinding the coil of the relay wasn't really too difficult, I decided to proceed with a repair instead. First, to access K-103, the transmitter bottom had to be removed. Then the bottom-rear panel can be removed and the two relays, K-103 and K-104 are mounted on the inside of that panel. I tagged all of the wires soldered to the 10 terminals on K-103 to make reinstallation easier and then unsoldered them and dismounted the relay. The relay coil is held in place with a single screw. Once the coil is out of the relay, then all of the original magnet wire has to be removed. By the way, the "break" in the wire never seems to be at the beginning of the wind. I just cut all of the original wire out with an Exact-O knife and remove it with needle nose pliers (or my fingers.) I measured the thickness of the original wire so I would know what gauge magnet wire I would need. The original seemed to be 33 gauge but all I had on hand was 32 gauge. >>>
| >>> I used a motor driven coil winder I had built about 30 years
ago. It's very basic in design and uses a "light dimmer" control as a
motor speed control for the small sewing machine motor. This allows me
to wind a solenoid-type coil pretty fast. I threaded an 8-32 stud into
the tapped hole in the coil spool so I could install that stud into the
chuck of the coil winder shaft - see photo below. You have to start the
winding slowly and this is where a variable speed motor control is
really necessary. Once the motor speed is about 100RPM, it is easy to
just use your fingers for tension and to also guide the wire onto the
spool. When it appears that the coil is about the proper dimension, I
stop the motor and clean a spot on the wire so I can measure the DC resistance
from the "inside" terminal to the clean spot - this would be the total DCR of the coil so far. I'm looking for
around 125 ohms DCR and when that is achieved, the coil is finished.
After the coil was wound, I wrapped it with black electrician's tape and
then lacquered the exterior of the coil. The original coil had "125"
stamped on the side, so I added that to this replica coil and then
mounted it back in the relay. Operation was just like an original relay.
Resoldering the wires to the relay was easy since all of the wires were tagged and their proper location readily found. After all the wires were connected and soldered, I coated the solder joints with the yellow-tinted lacquer to simulate MFP coating. Below are photos showing four of the steps to completing the repair of K-103.
Testing the CW Mode - The ART-13A was put back into the operating position and connected back up to the station antenna system. My initial test was on 3974kc, our Vintage Military Radio Net frequency, but since it was mid-day there would be no activity. This test showed that the ART-13 did indeed function in the CW mode now. The next test will be an actual CW QSO on 40M.
- It's hard to believe that the ART-13A in the photo to the right is the
same "parts set" shown at the beginning of this section. Though this
ART-13A turned out really nice and works great, let's consider what was
necessary to get the transmitter operational. First, I had to find an
Audio module - $67 with shipping off of e-Bay (and I had to repair/restore
it.) A set of three wire wound resistors - $45 from Fair
Radio. Plate Meter - $35 with shipping, Fair Radio. The MCW/FCI module
that was a spare had been purchased earlier for $30. The sheet metal
piece was $21. The total for missing parts was $198. Luckily, I didn't
have to buy any tubes. In addition to
that, figure that I had to spend about two weeks putting the transmitter
together and getting it operational. I still have to build an AC
supply specifically for this transmitter. Of course, I did essentially get this ART-13A as a
"freebie" that was included as a "parts set" for the Navy T-47. So, I
started with a "zero investment" but, as far as saving any money on this
project - that didn't happen. Unless you really enjoy all the aspects of
parts hunting, cosmetic restoration, mechanical reassembly, testing,
troubleshooting and repairing, it's probably
best to avoid these types of "basket case" projects. The positive side
is, of course, "bragging rights" to having saved another ART-13 from the
oblivion of the scrap heap.
UPDATE - ART-13A "Basket Case" - March 2013
>>> A method of securing the book to the chain and the chain end to the pocket were also needed. The correct chain was found at a specialty hardware store and the sleeving was salvaged from an old piece of rotor cable. I made a "fake rivet" out of a brass screw and nut for the attachment to the book pocket and then painted the "fake rivet" flat black. The installation looks very original with the right amount of patina. (See close up photo to the right.)
I was also able to remove some other items needed from a "parts set" ART-13 that belonged to KØDWC. The original Instruction Plate on the lower front panel was in poor condition but the "parts set" had one in nice shape. If you carefully drill the back of the rivets just enough to remove some of the rim they can be "punched out" with a small metal punch. This saves the rivets for reuse. The new Instruction Plate was mounted by installing the old rivets and then deforming the back of each rivet with a suitable punch. The front of the plate and the rivets have be held against a piece of hardwood to keep the rivets tight while punching. To fully secure the plate, use clamps to make sure the plate and rivets are tight against the panel and then apply a small drop of 5 minute epoxy to the back of the rivets. When that's cured, the plate will be secure and tight along with looking perfect.
I also replaced the mismatched meters with a set of matched Weston meters from the "parts set." Also, the original K-103 that I repaired was replaced with a good condition, functional K-103 unit from the "parts set." Also, the old "repaired" Interlock switch was replaced with a good condition, functional original.
I was given the OA-17 LF Oscillator as pre-payment for some work on a
T-368 transmitter that is owned by KØDWC. The OA-17 just about completes
this ART-13A "Basket Case" with the only other item needed being the
T-47/ART-13 "Restoration of a Typical Example"
This example of the restoration process features a very complete, good condition ART-13. Only minor disassembly and only one missing part made this restoration straight-forward and is typical of most ART-13 restorations today.
- The photo to the right shows the other ART-13 involved in the "Big
Trade." Though it looks to be another "parts set" it's actually in
pretty good shape. With this Collins-built USN T-47, all of the parts
were present except for the MCW/FCI module. The obviously missing meters
were carefully wrapped in bubble-wrap and in one of the parts boxes.
Knobs, the lid, and other minor items that were not on the transmitter
were in the boxes. The Audio Module was partially disassembled but this
was minor and only involved replacing some screws and nuts. Tubes were
carefully wrapped in one of the parts boxes. I found a MCW/FCI module
off of eBay. These are usually pretty cheap with this one costing $15
Reassembly and Body Work - This transmitter required the same sort of searching through the parts boxes but on a much smaller scale. All of the parts were easy to find since they were obvious items that were very recognizable. Note that the handle on the left side is bent. Actually, the sheet metal panel is bent. This required removing the handle and using a clamp and small wooden blocks to straighten. Even doing this carefully resulted in some of the paint chipping off. The area was painted with Krylon Black Wrinkle Finish using a small brush. Then the area was heated using a heat gun to activate the wrinkle. After the wrinkle had dried overnight, I matched the actual color of the panel with Artist's Acrylic paint.
Everything needed a good cleaning. I used Glass Plus for most of the cleaning. The wrinkle finish was cleaned using a soft brass brush and Glass Plus. Afterwards, Armor All was used to improve the looks of the original paint. The knobs were soaked in dish soap and water for about an hour and then cleaned with a tooth brush. Armor All can also be used on the knobs.
|Power Supply Construction and the Amazing Nemic-Lambda - I built a power supply entirely out of my junk boxes. It was a pretty standard for a tube rectifier design and used 866MV rectifiers for the +HV and a 5U4GB for the +LV. The unusual approach was to use a modern and very small Nemic-Lambda 10A power supply for the +28vdc. I saw this supply on eBay with a "Buy it Now" of $25. I couldn't resist the price so I purchased it. When it arrived I thought I had been sent the wrong item. It was about 3 lbs total weight. The size was 4"W x 4"T x 9"D. Nothing that small could provide +28vdc at 10A! A set-up and test proved to me that modern switching power supplies are amazing. I monitored the output with an oscilloscope and was amazed that the ripple voltage never changed from minimum load to maximum load. I left the Nemic-Lambda running the ART-13 +28vdc requirement for one hour with no problems and no over-heating. Also, older switching power supplies had a reputation for very noisy outputs with a lot of "switching noise" apparent on an oscilloscope when monitored. This Nemic-Lamba has no "switching noise" on the output whether at full load or no load. Simply amazing. The homebrew power supply is described in more detail below in "Hommage a le Valve."||Testing - Initial testing showed that this T-47/ART-13 worked with no issues. I was amazed that the transmitter had been partially disassembled and yet went together easily and worked on the first try. Initially, I used a fixed 400pf ceramic external capacitor to allow matching to my tuned dipole. I was able to get about 165 watts output with the transmitter but the audio sounded weak and under-modulated. I had selected the pair of 811 tubes for "matched" equal test results without too much regard for their maximum test readings. The T-47/ART-13 requires 811s that are at least measuring "minimum acceptable" to provide adequate modulation. Replacing these "weak" tubes with better (though not exactly matched) condition tubes resulted in great modulation characteristics.|
- This was the first T-47/ART-13 that I had worked on and restored to
working condition. It was a fairly easy project that took about seven
weeks to complete, including the design and building of the "Hommage a
Valve" AC power
supply. The power supply was actually at least 80% of the time required
to complete the project. This is normal in the restoration of your
"first" ART-13 since from then on you have the means to easily power-up
your next ART-13 projects.
At first, I had the Channel Selector switch set to MANUAL while I was learning how the transmitter operated. After a week, I started to setup some of the Autotune channels. I was generally operating on 3870kc or 3974kc and power output was about 160 watts.
For audio I used some military microphones at first but discovered they didn't fully modulate the ART-13 at the increased RF power. Although specific mikes are called for in the manual, these mikes can only be used if the carrier power is reduced to around 100 watts. I found that using a DH-50 crystal mike (with a Kobitone element) on an Astatic TUG-8 stand (amplified) provided fully adjustable audio drive with more than enough audio output for full modulation at 150 watts output power.
This ART-13 project was fairly easy and no serious problems were encountered. For the most part, if a complete and good physical condition transmitter is purchased, this will give you the best chance of completing the project with very few, if any, problems.
|UPDATE - Collins T-47/ART-13
- March 2013 - The T-47/ART-13 is now
located in the upstairs radio room in Dayton, Nevada. We have set up
this ART-13 transmitter to run with the Solid-State Dyna-Sim AC Power Supply which
"stacks" a +400vdc power supply and a +900vdc power supply to allow
the +HV to run around +1300vdc. This "series" method is how the
dynamotor achieves its +HV and the power supply can be built using
easier to find parts. The plans for building this type of AC
power are below in the "Homebrewing an AC Operated Power Supply
for the ART-13."
To the right of the ART-13 is the RCA CGR-32-1 receiver built for the U.S. Coast Guard in 1940. These receivers were special built versions of RCA's AR-60 receiver. The receiver is connected to the LS-112 on the wall that's out of the shot.
Above the Dyna-Sim power supply is another auxiliary variable capacitor. This air variable has not been painted - yet. I typically run the T-47 with the Shure Bros.102-C carbon microphone to provide the listeners with an authentic "military sound" to the signal.
Homebrewing an AC Operated Power Supply for the ART-13
Three ART-13 power supply approaches are presented here. The first two versions provide separate +HV and +LV supplies along with +28vdc supply. The first is a "Brute" of a power supply where space and weight are not a consideration but high plate voltage and stability are the primary goals. The second power supply, the "Hommage a le Valve," is a typical VT approach to building an ART-13 power supply that doesn't stress the transmitter, only providing +1400vdc for the +HV. This power supply is much smaller and only weighs about 75 pounds. The last section provides details on how to build the "Dyna-Sim," or Dynamotor Simulator, that uses series +HV and +LV power supplies (aka "stacked" supplies.) This method allows the builder to use smaller, easier to find components and still provide about +1200vdc (or more) plate voltage. Schematics for all three types of AC power supplies are provided.
- I built the electronics portion of "The Brute" for KØDWC (who did
all of the work on the mechanical portion) to use with his ART-13A with the idea of
gaining maximum power output with massive components for "rock-solid"
stability. This power supply consists of a huge 1760vac CT @ 500mA Plate
Transformer using a Choke-input filter to provide about +1680vdc HV. A
+400vdc power supply uses a dual section filter for low ripple. The
+28vdc is provided by a Meanwell switching-type power supply rated at 13 amps.
These are set to their maximum voltage output of +26.5vdc. The
bottom section of the power supply contains most of the +1680vdc components. The
top platform contains one of the HV chokes, the +400vdc and the +28vdc power supplies. PTT and
Power ON relays along with the 100W bleeder resistor are also mounted
underneath the top platform. All outputs and
control lines are wired to a U/7 type box connector so that
connection to the ART-13 requires a cable similar to the original
dynamotor cable, that is, with U/7 plugs on each end. A screened cage
covers the entire power supply for safety. Due to the weight of this
"Brute," casters were added to the bottom and moving the unit around is
actually quite easy.
+1680vdc - Features a very large plate transformer that easily will handle 500mA continuous duty. This results in a very stable +HV for the transmitter. Solid State Microwave Oven diodes (NTE517) are used for rectifiers and two 2500wvdc rated oil filled capacitors in combination with two large chokes make up the Choke-input filter. A large 40K 100W bleeder resistor is used on the output.
+400vdc - This supply uses a large power transformer rated at 200mA. Again, SS Microwave diodes are used (though not necessary) but this time a dual-section filter is used. This consists of three series combos of two 40uf electrolytic capacitors in series to get the working voltage up to 900vdc. 470K resistors are across each electrolytic to even out the voltage drop.
+26.5vdc - This is provided by a Solid State commercial power supply rated at 13Amps. This modern switching power supply has a cooling fan that changes speed depending on the current demand. Manufactured by Meanwell. All output wires must be shielded for potential RFI problems.
Relays - Two 28vdc relays provide "Power ON" function for the ART-13 and the Push-to-Talk function.
Fuses - All inputs and outputs are fused for full protection.
Meters - No meters are provided on the Brute
Pilot Lamps - These are vintage 120vac lamps. Amber indicates that the +28vdc power supply is turned ON. When the ART-13 is switched ON a relay actuates and connects +28vdc to the ART-13 U-7 plug. The Red lamp indicates that AC primary voltage is routed to the PTT relay and that +LV and +HV will be routed to the ART-13 when PTT is actuated.
Plate Current Meter Shunt - This is a large Ohmite 25 ohm pot rated at about 25W. It can be adjusted to 20 ohms for a 1X meter scaling or set to 1.5X or 2X if desired.
Cage - This large metal screened cover protects the user (or pets) from accidental contact with the +LV or +HV circuits. Since the "Brute" is designed to set on the floor, it is located far away from the ART-13 and no magnetic coupling issues will be experienced.
|Hommage a le Valve
- This is the first ART-13 power supply that I built. I decided to go
tube rectifiers for the +HV and +LV. The +28vdc is provided by a very
small Nemic-Lambda switching power supply. I didn't want to really push
the T-47/ART-13, so I was shooting for about +1400vdc for the +HV. I
happened to have a "parts set" that originally was a relatively small 813
transmitter. This piece of equipment provided the +HV iron and many
smaller parts. This 813 transmitter was housed in an old S-47 Hallicrafters
cabinet that was also utilized. I installed a "butch-plate" on the
"stripped" 813 transmitter chassis and this became the new chassis for
the power supply. Another "parts set" homebrew high-power audio
amplifier supplied the +400vdc iron and a few more parts. All of the
smaller parts like relays, meters, etc. came from the junk box. I
decided to use a large terminal strip for the outputs on this power
supply. This then allows building a cable that only uses one U/7 plug.
I decided that since 866A MV tubes were going to be used I should have a "viewing port" to watch the "blue glow" of the tubes. Full metering was also provided only because I happened to find a matching set of three meters in one of the junk boxes. A 5U4GB has to be used for the +400vdc due to that tube's rating being at a high enough current and operating voltage for that application. Since tube rectifiers were used, I provided the filament voltages with separate filament transformers. This allowed the tube rectifier filaments to be "on" at all times but to use the PTT from the ART-13 to apply the +HV and the +LV via the power transformers to the rectifier plates. This simulates the operation of the dynamotor starting up with actuation of the ART-13's PTT.
+1400vdc - Relatively small plate transformer salvaged from old homebrew 813 transmitter. 866A MV rectifiers utilizing a 2.5vac 10A filament transformer. Pi-filtered.
+400vdc - Power transformer from homebrew audio amplifier. 5U4GB rectifier. Dual section filter.
+28vdc - Nemic-Lambda +27.5vdc rated at 10Amps, a small switching power supply of modern design. Actually this power supply is a 24vdc power supply and is adjusted up to +27.5vdc using the voltage adjustment pot provided on the rear chassis of the unit. 40mv of ripple regardless of load. RF quiet. Even so, all output wires must be shielded for RFI quite operation.
Relays - Two 28vdc relays for ART-13 power ON and PTT function.
Fuses - Fully fused on all inputs and outputs
Pilot Lamps - High intensity clear LEDs provide illumination inside vintage "jewels." These LEDs were purchased at Radio Shack. When operating these LEDs on AC, a diode will be needed along with the appropriate load resistor. As seen below in the photo, the red and yellow lamps only illuminate when the power supply is providing +HV and +LV to the ART-13. The blue lamp indicates that the ART-13 is "ON" and ready to use. The left green lamp indicates that AC is applied to the +HV/+LV section and the rectifier filaments are powered. The right green lamp indicates that the +28vdc supply is "ON."
Meters - The +HV and +LV meters only indicate voltage when the ART-13 is in operation. The +28vdc meter indicates that voltage as supplied to the ART-13 and is in continuous operation while the power supply is "ON."
Plate Current Meter Shunt - I used a 40 ohm 25W Wire Wound potentiometer that had a 25 ohm 25 watt WW resistor in parallel with it. This allows easy adjustment to 1X, 1.5X or 2X of FS reading on the Plate Current meter. The excessive dissipation of the shunt is just a safety factor since this is the only path for -HV to chassis. Failure of this shunt would allow full -HV current to flow through the meter (which is not good.)
Cabinet - Hallicrafters S-47 painted black wrinkle finish. Tag found in the junk box. Since this cabinet is steel and is grounded, the ART-13 can set on top and there will be no 60Hz AC to audio chain magnetic coupling problems
Schematic for the Brute
By comparing the two schematics, it is obvious that going solid-state is a much easier approach to building an AC operated power supply to operate the ART-13
Schematic for Hommage a le Valve
The Dyna-Sim - "Dynamotor Simulator" - Series +HV and +LV Power Supplies
|For many months now, every few weeks I've been
switching in and out of the operating position one of my two ART-13
transmitters because only one AC power supply was available. After I
finished the restoration of the ART-13A "Basket Case," I
didn't design and build a power supply for it. This situation needed to
change. I decided that I didn't want to go the huge,
immoveable type of power supply but that I would rather design a power
supply that was small and lightweight. I wasn't concerned about maximum
power output since I had the "Hommage a le Valve" power supply that easily
allowed running 150 watts output from the transmitter. This new power
supply would be like the dynamotor in that two lower voltage supplies
would be connected in series to provide the +HV and I would shoot for
about +1150vdc as the dynamotor supplied.
The original dynamotor circuit provided +400vdc for the +LV and +750vdc (+HV) in series with the +LV to achieve +1150vdc plate voltage. A barometric pressure switch separated the two supplies above 25,000 feet altitude to prevent arc-over by reducing the plate voltage to +750vdc. It is very easy to use this same approach in designing an AC operated power supply, excluding the barometric pressure switch, of course. The advantages are that the components used will be rated at lower voltages which reduces expense and generally makes locating them easier. One thing to keep in mind is that the +LV supply must be able to handle not only its own current requirements but must also be able to carry the current required by the +HV since the negative return for the +HV is connected to the +LV and then to chassis. This means that the +LV will have to be capable of about 500mA maximum current. The original dynamotor spec for the +LV is 750mA but this is the dynamotor capability not the actual +LV current requirement of the ART-13.
To handle the additional current the +LV transformers are actually two identical transformers that are connected in parallel. When operating transformers in this manner they must be exactly the same,... identical. Also, their connections must be "phased." This means that primary and the secondary windings must be connected so the AC applied and the AC output are in phase in each transformer. This is easy to test ahead of the building and mark the primary and secondary windings so there will be no confusion at assembly time. I only used the parallel transformers because I didn't have a single 400-0-400vac that had enough current capacity for the +LV requirement. If you can find a 500mA rated transformer then going with the single, although large, transformer is much easier. Same reason for the parallel chokes in the +LV supply.
There are some changes that have to be made in the general design that allows for the proper operation of the Plate Current meter since the -HV is connected to +LV. This is basically done by providing a bridge circuit using a 13.4 ohm series load from -HV (negative meter connection) to pin 1 (+LV) and a 6.7 ohm series load from pin 1 (+LV) to pin 9 of U7 (positive meter connection.) This duplicates the circuit used in the original dynamotor. The advantage to this bridge resistor set up is that the Plate Current meter reads accurately regardless of the actual level of +HV and +LV as long as the ratio of +HV to +LV remains approximately 2:1 (actually, the ratio of +750 to +400 is 1.87:1 but the bridge resistor ratio is 2:1.)
Since a minimum of +750vdc is used for +HV, the filter capacitors can be series-connected 100uf 450wvdc type electrolytics with 510K resistors across each cap to equalize the voltage drop across the series connections. Three capacitors are used resulting in a working voltage of about 1350vdc at a capacitance of about 33uf. Since we are using Pi-filtering, in an "unloaded" condition the +HV could soar to around +1035vdc.The extra "head-room" is protection in case the power supply is operated without a load. The same type of "head-room" is used in the +LV section, where the unloaded voltage could rise to around +600vdc. Using two series-connected 350wvdc electrolytics results in around +700vdc capability. In normal operation, the power supply design is such that the +HV and +LV are actuated with the PTT from the ART-13 which would also be in the powered-up condition thus presenting full load to both the +HV and +LV instantly. However, in some testing situations (or perhaps in an ART-13 failure mode) the power supply might be operated "lightly loaded" (or "unloaded") and this capacitor "hook-up" gives us the necessary head-room to survive this possibility without component damage to the power supply.
Solid-state microwave oven type diodes can be used in both supplies connected as full-wave rectifiers. These diodes are type NTE517 rated at 15kv PIV. These diodes are relatively expensive at about $6.00 each. The advantage of SS diodes is higher output voltage from the power supplies.
To take advantage of the smaller size and lighter weight possibilities, a 24vdc 13 amp Meanwell Switching Power Supply is used for the +28vdc requirements. This supply can be adjusted up to +27.0vdc maximum which will provide sufficient voltage to operate the filaments, relays and the Autotune. Though the Meanwell PS is RFI quite as a +27.0vdc source for the ART-13, it can cause interference in receivers unless the cable from the power supply to the ART-13 is fully shielded. I've used this model Meanwell on two different ART-13 power supplies and there is no interference in either the transmitter operation or in the receiver being used. The Meanwell PS is approximately 2.5" x 4" x 8" and weighs about 3 lbs. This is the same type of PS that we used when building "The Brute" ART-13 power supply. The Meanwell PS is generally available on eBay for about $25 plus shipping.
I decided to build the Dyna-Sim into a BC-348 cabinet. This cabinet had been destroyed by a former owner who drilled out all of the pop rivets that mount the bottom plate which has all of the engagement pins for the shock mount. Rubber feet were installed to take the place of the engagement pins, thus ruining the cabinet for proper use with a BC-348 and FT-154 shock mount. The back of the cabinet had have a wide rectangular opening cut to provide access to the fuses, line cord and the output terminal strip. A round hole was also cut to provide ventilation for the fan in the Meanwell PS. The front panel is made from type of black hard plastic called delrin. Three panel meters are provided to allow constant monitoring of the output voltages during operation. >>>
>>> As with the "Hommage a le Value" power supply, the only reason I used three meters is because I found three matching meters in the junk box. Setting up any DC current meter to act as a DC voltage reading meter is quite easy and only involves knowing the meter coil resistance, the meter full scale current requirement and then calculating a series dropping resistor based on the supply voltage to be measured versus the FS voltage scaling desired. For example, if the meter to be used is a 1mA FS DC Current meter and it is going to be used to measure the +400vdc and the FS DC voltage scaling desired is +1000vdc. The DCR of the meter coil in a 1MA FS meter is usually around 50 ohms (but measure it to be exact when actually doing your calculation.) Since the meter is 1mA FS, the total current through the series dropping resistor and the meter will be 1mA. The meter coil resistance is 50 ohms, so E = I/R indicates that the voltage drop across the meter at FS will be .00002vdc. FS DC voltage will be 1000vdc, so 1000 - .00002 = 999.99998 drop required in the series resistor. R=E/I so 999.99998/.001 = 999,999.98 ohms. You might as well use a 1 meg resistor. Dissipation equals I² x R = P or (.001 x .001) x 1,000,000 = 1.0 watt. 2X the dissipation is standard practice and allows the resistor to operate in the middle of its rating. So, a 1 meg ohm 2 watt resistor can be used and the 1mA DC Current meter will read accurately the +400vdc at .4mA on the scale. You can usually alter the actual meter scale so that "MILLIAMPS" is painted over and leave the "DC." If you have suitable "rub-on" lettering, you can add "VOLTS" to complete the meter transformation. To take advantage of the existing meter scale, the +HV meter actually indicates the +750vdc supply measured to -HV rather than measuring to chassis which would indicate +HV plus +LV, or the actual voltage applied to the 813 and two 811 plates. (I've been thinking lately that the +LV meter could be replaced with a +HV current meter. This would allow monitoring total +HV current and voltage simultaneously. Probably much more informative than monitoring the +LV that seldom changes. I'll update this section if I do the modification. - H.Rogers Apr 2013)
Two 24vdc relays are required for the PTT and Power On functions. The junk box turned up a very nice heavy-duty dual relay with 0.25" contacts. The problem was that the coils were for 115vac operation. Since these are solenoid coils, the operation doesn't really change whether AC or DC voltage is used. When using DCV on an ACV rated coil, you will have to greatly reduce the voltage. In testing the relay, it was found that good switching occurs with about 15vdc. A 150 ohm dropping resistor in series with the +27vdc supply provided around 18vdc to the relay and allowed fast, positive switching
A construction technique employed in the Dyna-Sim is the use of "component boards." The boards were made of 3/16" thick delrin and the terminals were made from 4-40FH brass screws secured with brass nuts. The use of brass allowed soldering directly to the terminal stud. Unfortunately, component boards require a lot of planning for proper layout and routing of the wiring (which is via a harness.) This prolongs the design phase and ends up with the project taking much longer to complete. If you're in a hurry then the use of standard tie points is easier and allows for quick construction. The upside of component boards is that the appearance of the wiring and construction looks like a professional job. See photos below of the finished Dyna-Sim.
+750vdc (+HV) - This is supplied by a 1475vac CT Plate transformer rated at .25A. Since no other windings are on the frame, this transformer is relatively small. Pi-filtered. Actual voltage is close to +900vdc under load. Total +HV is approximately +1300vdc.
+400vdc (+LV) - This is supplied by two identical parallel-connected 780vac CT Power Transformers and two identical parallel connected filter chokes. Actual voltage is around +440vdc under load. Total current available is 500mA. Pi-filtered.
+27.0vdc - This is provided by a Meanwell Switching Power Supply rated at 13A. Very small. Apparently not all Meanwell 24vdc power supply maximum voltage outputs are the same. Usually +26.5vdc is the specification for the maximum adjustment but this one adjusts to just over +27vdc. Fully shielded wires for RFI quite operation.
Relays, Fuses & Meters - Two 24vdc relays are used for PTT and Power On functions. The AC input and all outputs are fused. Three meters allow for constant monitoring of the voltages during operation.
Plate Current Meter Bridge Resistors - This is an original combination WW resistor from a junk DY-17A dynamotor base.
Pilot Lamps - High intensity LEDs with vintage-type jewels are used. Red = +HV, Yellow = +LV, Blue = ART-13 Pwr ON, Green = AC power ON to +28 supply and to +HV & +LV supplies.
Cabinet - Derelict BC-348 cabinet with black delrin front panel. The "cool" tags were donated by KØDWC and KE7MFW. Cabinet was painted with VHT Black Wrinkle Finish paint.
NOTE ON CABINET: Since the BC-348 cabinet is aluminum (and the Dyna-Sim panel is delrin) and the case of the ART-13 is aluminum, no protection is provided for magnetic coupling from the transformers in the power supply. When installing the power supply be sure it is not placed directly next to the right side of the ART-13. Since this is where the ART-13 Audio Module is, very likely magnetic coupling will occur and cause some 60Hz hum to appear on the signal in the VOICE mode.
|Initial Testing of the Power
Supply - After any one of these power supplies is built
it will be necessary to perform some tests before actually connecting it to a
transmitter. This will
require attaching some "hefty" load resistors for the +LV and +HV
supplies. The +28vdc doesn't require a load since the Meanwell is
voltage regulated and remains constant regardless of the load.
With the +28vdc operating check the operation of the two relays that operate the "Power ON" function and the PTT function.
This will require using some test leads for the connections to simulate
what the ART-13 does in operation. You can use a separate +28vdc bench
power supply to actuate the PTT, otherwise, using a test lead connect
PTT + (pin 3 U/7) to the +28vdc and ground pin 8 U/7 with a test lead to
actuate the PTT.
The +HV and +LV will require calculating a suitable load resistor for each supply. By using the expected voltage as E and the amount of current drawn as I, then E/I=R, which will give you the resistance value for that amount of current to be supplied by either the +HV or the +LV supply. Use I²R=P to calculate the amount of watts the resistor will have to dissipate. You'll find that the load resistors must dissipate around 100 watts, so large wire wound "Ohmite-type" resistors are required. Use good clip leads to connect the load resistors to the output terminals. Apply the power supply AC voltage and actuate the PTT. This will apply AC to the +LV and +HV transformer primaries. Measure both the +HV and +LV to see what the actual voltage "under load" is. Let the power supply run for a few minutes and then deactuate the PTT and turn the power supply off. This checks the most important part of the power supply. Use about 225mA or so for the +LV load current and about 130mA for the +HV load current.
Once these tests have been performed, attach the U/7 connector to the ART-13 and power it up. If you are using the power supply with a known operational ART-13 that is already connected to an antenna, you should be able to do a test of the entire operation of the power supply and see how it works with the transmitter. If you are going to use the power supply to troubleshoot an unknown condition ART-13, then you might be blowing some fuses. That's why fuses are in the circuit - to protect your power supply. Use only the fuse current rating necessary for reliable operation in the fuse values you select. Fuses "blow" because of the relationship of their internal resistance versus the current flow through the fuse. I²R=P and P (watts) is what blows the fuse. The voltage shown on the fuse is the design rating for the fuse structure and type of housing. It's the current change that "blows" the fuse since the circuit voltage and the fuse resistance remain constant (until the fuse "blows.") So the appropriate fuse current rating is just slightly higher than the normal current demand of the circuit being powered.
IMPORTANT NOTE ON THE MEANWELL POWER SUPPLY - I've never experienced any RFI noise problems with the Meanwell switching power supply when used with the ART-13 as the source of +28vdc at 10A. That being said, I've noticed that if the Meanwell is used to power up a receiver, for instance the R-392, fairly noisy operation will result. This situation was experienced when the power connecting wires from the Meanwell power supply to the receiver were unshielded. Although the receiver and the power supply were grounded, the connecting wire for +28vdc was unshielded and could thus radiate some RFI noise. I'm sure that the reason I don't have any receiving noise when using the ART-13 is because the Meanwell power supply is shielded within the homebrew power supply (HB PS) cabinet and is grounded to the chassis of the HB PS and the connecting cable from the HB PS to the ART-13 is fully shielded. So, when using the Meanwell on some DC operated gear you may find that if your connecting wires are unshielded you'll have some interference in the equipment or in nearby receivers. However, with a fully shielded cable that interference is eliminated.
Using the ART-13 on the Ham Bands Today
The ART-13 Audio Module has a "fixed-level" gain setting that was designed to
work with specific WWII vintage military microphones with the ART-13
operating at its standard voltage levels available from the dynamotor.
There are a couple of carbon microphones specified and a couple of
dynamic microphones also specified in the ART-13 manuals. The Shure
Bros. Co. T-17 was probably the most commonly used carbon microphone by
Many ART-13s will be found with the CARBON/DYNAMIC switch "safety wired"
to the CARBON position.
Carbon Microphones - There are two problems that are normally encountered with carbon microphones. First, the military expected the radio operator to "scream" into the microphone. After all, he was trying to talk over the aircraft noise and was probably being shot at! Second is that many vintage carbon microphones don't have the output they used to. Most military WWII carbon microphones will not allow enough audio for proper modulation due to "carbon packing," "carbon fusing" or other age and use related factors.
Though the ART-13 manuals will specify a couple of microphones to use with the transmitter, nearly always (if you happen to have the particular types) you'll find they don't provide enough response to fully modulate the carrier. For Carbon mikes you'll have to test several examples to find an element that still has proper response and has not been ruined with excessive bias voltage (which causes the carbon particles to fuse together.) You can buy replacement carbon elements but many times these are of old manufacture that just haven't been used (NOS) but they don't seem to work any better than the well-used older elements. This is probably due to "carbon packing" - another common problem. It's also possible to buy new carbon mikes that do seem to work very well because they haven't been subjected to any abuse and also the carbon particles haven't had time to pack together. Typically, you'll end up testing a lot of carbon mikes before you find an acceptable example.
Other Microphones - There are also Electret microphone elements that are a modern condenser microphone with a built-in transistor amplifier. It is possible to use the ART-13 mike bias voltage to power an Electret microphone. This method can be used to replace a carbon microphone. There are many Electret circuits available "on-line." Many Dynamic mikes usually don't seem to fully modulate either but many times this is due to a mismatch of the impedances. Try to find a Dynamic mike that has an output impedance of 250Z ohms which is what the ART-13 is designed for. You might find that some of the newer 500Z ohm dynamic elements are also a good input Z match.
|IMPORTANT NOTE on Output
Power vs Audio Modulation - If you are running your
ART-13 on the dynamotor you'll get about 100-110 watts maximum output power.
The +LV will be around +400vdc and the +HV will be around +1150vdc. You
will probably have no problem running good condition military carbon
mikes or low-Z dynamic mikes with this type of set-up. If on the other
hand you are using an AC power supply that provides increased +HV levels
for increased RF power output on the ART-13, you might find that no
carbon mike will fully modulate the carrier. When using any of the
microphones it will probably be necessary to adjust the ART-13 output power to
compensate for the increased ratio of RF power to audio output from the
ART-13 Audio Module.
Although the +HV has been increased to provide higher RF power, the +LV
might still be at around +400vdc which limits the audio output levels from
the Audio Module and thus the audio drive to the modulator tubes. The
result is you can't seem to ever get enough out of the mike you are
using. To actually see what is happening you should use an oscilloscope
to monitor the transmitter's output waveform to see what the modulation
level is. Using a vintage military carbon microphone you will probably see around 80%
modulation (or less) if you're running at, for example, 150 watts output.
Try reducing the RF power output until you see the oscilloscope showing around 100%
modulation. You'll probably find that the ART-13 is now running around
100 watts output, which is what the design output level was using the
dynamotor as the +HV and +LV source. With the AC power supplies, even though the modulator plate
voltage is also at the higher level, the +LV usually isn't. This results
in minimal audio drive using stock microphones. It is possible to build
your AC power supply to increase the +LV. About 10% increase is safe and
will allow better performance using carbon mikes up to about 150 watts
carrier power. If you want to run even higher carrier power then you're going to have to increase the audio level as described in
the following method,...
The Easy Microphone Solution - The easiest method to have high output from the microphone, that allows you to run the ART-13 at a higher power output with 100% modulation, is to use a preamplifier between the mike output and the transmitter input. The Astatic TUG-8 mike stand is the easiest way to provide a preamplifier since a battery operated one is in the base of the stand. You can use any of the Astatic mike heads, e.g., 10-D, D-104, T-3, etc., and with the TUG-8 stand, these mikes will all sound fine and provide plenty of output. The preamplifier output Z is a fairly close match to the Dynamic input Z. Be sure to have the switch in DYNAMIC when using the TUG-8. Also, watch your transmitter's output waveform on an oscilloscope to set the TUG-8 "gain" control to proper level of modulation. The "gain" control is adjusted by a slotted shaft potentiometer that is accessed via a hole in the bottom cover of the TUG-8's base.
To Sum it Up - On AC power supply operated ART-13s, to run original military type carbon mikes, reduce the carrier power on your ART-13 until you are able to achieve 100% modulation. If you want to run at higher carrier power then switch the ART-13 mike switch to DYNAMIC and use an amplified mike. Then adjust the mike gain for 100% modulation.
|Operating AM (VOICE) - Initially, an oscilloscope must be used to determine if the microphone chosen is really a suitable one for the ART-13. The oscilloscope will almost instantly show you whether or not you are achieving 100% modulation. The easiest way to use the oscilloscope as a "modulation monitor" is to connect a "pick-up wire" to one of the vertical amplifier inputs. The length of the "pick-up wire" will be depend on your power output, location of the antenna and how much vertical amplification you use on the 'scope. Most of the time a three foot wire works fine, sometimes you might have to use a 10' wire - experiment with what gives the best 'scope pattern. While transmitting in VOICE, adjust the 'scope for a modulation envelope pattern and you will almost instantly see if you have full modulation. Just a slight "touch" at negative 100% is seen as either a slightly brighter "dot" at zero or a short "line" at zero. Both are indications that the ART-13 is modulating to 100% negative and you don't want to go any further than that with your audio drive level. Note the positive excursion also. This should be symmetrical and at 100% positive. If you find that you are not achieving 100% positive but are at 100% negative modulation you might have weak 811 modulator tubes. Also, it's possible that there is some excessive current being drawn on the +HV which limits the positive peaks of modulation. You can reduce carrier power somewhat and see if that helps with the modulation symmetry.||Operating CW - Many ART-13 owners don't operate the transmitter in the CW mode. This really isn't because of a lack of CW experience but mainly because there are some limitations to "comfortable" operation in the CW mode. The ART-13, like most military transmitters, uses a Keying Relay to provide many functions inside and outside the transmitter. Outside the transmitter would be the Antenna switching and Standby function between the ART-13 and the receiver that provides "break-in" operation in CW. However, the Keying Relay is noisy - no doubt, on the airplane it was probably barely noticeable, but the typical ham shack will be a cacophony of racket when the ART-13 is transmitting CW. Also, if you're a fast CW operator, the Keying Relay will limit your speed. Although the ART-13 manual says that 30 wpm operation is possible, 15 wpm is a more realistic "speed limit." There are some modifications to eliminate the Keying Relay operation in CW and key the various circuits directly but one would have to decide whether or not the CW mode on an ART-13 was going to be a major facet of operation that would justify "hacking up" the transmitter. Besides, operating the ART-13 in CW in the original configuration provides the user with some of the experience that the airborne radio ops had to endure.|
|Antennae, Auxiliary Condenser
- The ART-13 is not a ham transmitter, so it's not surprising that it
doesn't readily operate into a dipole or quarter-wave vertical antenna.
One of the idiosyncrasies of the ART-13 is that it was designed to
operate into antennas found on aircraft. This was usually either a 20-60
foot end fed wire
from the front of the plane to the tail, or a 200 foot long trailing
wire antenna that was also end fed. Sometimes short whips were also
used. Anyway, it's likely that no ART-13 every originally operated into
the 50 to 75 Z ohm unbalanced, low reactance (mostly resistive) type load that most ham antennas provide. The
common solution is to add approximately 200pf to 800pf of capacitance from the COND terminal to the
GND terminal which then provides a Pi-Network
of sorts in Tuning positions 1 to 6. In positions 7 to 13, a Pi-network
is already provided and usually above 7.2mc an auxiliary condenser shouldn't be
required. Most amateurs operate the ART-13 in the 80-75M and this will
require additional capacitance.
If you operate on just one frequency in the 80-75M band, then a fixed value capacitor can be used. It's also possible to provide several fixed value capacitors to provide optimum loading on several frequencies. It's also possible to use a transmitting air variable capacitor which will allow optimum setting of the antenna loading and any frequency or any tuning range. Most transmitting variables are about 350pf maximum capacitance and will require a capacitive shunt to increase the maximum value to around 800pf depending on exactly where you want the antenna loading to be set. Most users find that around 500pf works quite well on 80M. It will depend on exactly where you want to load up the ART-13 considering the power supply's current availability provided for the +HV and the ART-13 power output desired. (See section below "Construction of a Variable Auxiliary Capacitor Set-up" for a description and photo of a method of mounting an suitable variable capacitor for this purpose.)
SWR - Be sure when loading the ART-13 into an antenna that you use the lowest setting of C that allows tuning the transmitter to the antenna load. Although you can find higher settings of C that might appear to tune to the antenna, you might actually be tuning the transmitter to a harmonic instead. If you have an SWR bridge in the antenna line, look at the SWR and, if the antenna is matched for say 80M and you show a low SWR, then the setting of C is okay. 40M operation is very prone to tuning to a harmonic - watch your SWR and monitor your transmitting frequency.
Frequency Monitoring and Zero Beating - The easiest way to monitor the frequency of the ART-13 is with a digital frequency counter. The Counter can have a short "pick-up" wire connected to the input and that should provide sufficient signal for the Counter to operate on. Normal AM net operations are on specific frequencies so it's rather easy to set the ART-13 up before hand.
If you have to do a minor adjustment to the frequency merely unlock the locking bar on Control B and fine tune the transmitter to the correct frequency. Be sure to re-tighten the locking bar afterwards. If you have the transmitter in MANUAL you can just adjust B to the correct frequency (leaving the locking bar tight.)
If you have to zero beat a signal for some reason you'll find that the transmitter signal output in CALIBRATE is pretty strong. Normally, the CALIBRATE signal will over-power the incoming signal on the receiver. It is possible to tune the ART-13 to the highest S-meter reading and you'll be close enough for AM. If the incoming signal is a strong one, you'll be able to hear the beat note and adjustment is easy then. (see ARC-8 set-up below for more info on CALIBRATE.)
The ART-13 doesn't drift very much. Normally about 1.0kc in about 1 hour is usual.
BC-348 Receiver Operating with ART-13 - ARC-8 was the designation for one of the most common set-ups for aircraft use of the ART-13 and combined it with the popular BC-348 receiver. Today, many hams run the ARC-8 configuration as it provides an aura of authenticity to a vintage military radio station (and the BC-348 is a great performing receiver.) The BC-348 can be wired into the U-8 socket on the ART-13 to provide full break-in operation. Use pins 23 and 24 on the ART-13 U-8 socket* to provide a NC connection to pins 3 and 4 on the PL-103 connector on the BC-348 which will allow the ART-13 to control the stand-by function. One disadvantage to this set-up is that it will require using a separate frequency monitor such as a Heterodyne Frequency Meter (e.g., BC-221) or a digital frequency counter to know the ART-13 transmitting frequency. When the ART-13 is switched to CALIBRATE, the BC-348 will be muted thus you won't be able to zero beat any received signals. Since the BC-348 dial wasn't particularly accurate, the military wanted you to use the BC-221 to set up the transmitter frequency or to use the ART-13's on-board FCI module to calibrate the transmitter frequency. So, the fact the the receiver is put into stand-by is standard for the CALIBRATE function on the ART-13.
*Pins 23, 24 and 25 on the U-8 socket access the internal sending relay in the ART-13. Pin 23 is Common (arm,) pin 24 is NC and pin 25 is NO. You can also use pin 23 and pin 25 to provide a "Break-in" for the R-390A receiver.
Physical Location and Shock Mounts - There are a couple of different shock mounts that were used with the ART-13 transmitters. All of them are beyond difficult to locate. Probably when the transmitters were removed from service, the shock mount was left behind and scrapped with the airplane. Today, ART-13 transmitters are rarely offered or found with an original shock mount.
When placing the transmitter in its location in the station you will have to simulate what the shock mount provided. Not the vibration dampening but the elevation of the transmitter up off of its bottom plate. This elevation was how the ART-13 cools itself - by convection. Use spacers made of wood or rubber to raise the transmitter up so there is at least one inch of clearance between the table and the bottom cover. This is usually enough to allow air flow and cooling.
|Loading up the
ART-13 on 75 Meters - If you read the loading instructions in the
ART-13 manuals you are sure to be confused since these are written for
operation with aircraft antennae. Hams generally are using a dipole
antenna which will tune differently. First, make sure you have an
auxiliary capacitor connected to the COND terminal to the GROUND
terminal. This can be a fixed ceramic HV cap of around 500pf or a
transmitting air variable that provides adjustable capacitance from 30pf
up to 800pf. Depending on your air variable, you may have to use shunt
capacitors to get up to 800pf.
1. Adjust Control
E to 200 - minimum capacitance
These are the steps to load the ART-13 up to a tuned dipole antenna using a variable air capacitor as the Auxiliary Capacitor. When using a fixed capacitor, you won't be able to vary the loading as much. Use Control E to see how much variability in loading you have. You can only increase capacitance with Control E if it was set for 200. This will increase the plate current in the configuration used on 80M. Normally, the value of the "fixed" Auxiliary capacitor is chosen to give some adjustability on Control E for the desired loading for the frequency and antenna used.
NOTE: The ART-13 loading will vary somewhat depending on the level of +HV used. This description applies for +HV levels around +1400vdc. Higher or lower levels of +HV will result in slightly different resonant points for Control D.
|40 Meter and 20 Meter Operation -
Operation on 40M is basically the same as 75M except that Control
be advanced up to triangle #8 or higher. At this point, the output network is
actually a Pi-network and although the auxiliary capacitor
probably isn't required, it does make loading much easier if it is used.
Interestingly, the 40M band seems to be split with Control
referencing 7.2MC as the point of change. Usually, when operating in triangle #8 on Control
A the lowest frequency tuned
is about 7.15MC so you won't be able to tune into the CW portion of the band. Switch to triangle #7 on Control
A for operation
in the CW portion of the 40M band and you'll find that entire 40M band
can be tuned. You might find that the Grid Drive Current is down a bit
on 40M, since the alignment procedure allows for reduced Grid Drive at
the band edges.
If you experience arcing inside the transmitter on 40M but not on 80M, it's probably a loading problem. Reset the position of control C first. If that doesn't help, try reducing the loading for lower total plate current.
|30 Meter CW Operation - Since the ART-13 is continuous coverage from 2.0MC up to 18.0MC, it's possible to do some CW operating on the 30M band. This is a small segment from 10.100MC up to 10.150MC available for ham operation in CW/Digital modes only. Naturally, a general coverage receiver will have to be used in conjunction with the ART-13. Since most hams are using tuned dipoles for an antenna, be aware that these normally will work fine on harmonically related frequencies but will not allow loading on 30M. I just use a separate small dipole specifically cut for 30M. Dimensions are 23 feet per leg and I feed the antenna with coax and a 1:1 balun. Be sure to check the "30M Band Plan" PDF file because each segment of the 30M band is allotted to specific functions and modes. Also, 200 watts is the maximum power.|
|Construction of a Variable Auxiliary Capacitor Set-up - By far the best method of providing the additional capacitance required for dipole antenna operation below 7.0MC is to use an air variable. The variable capacitor allows very careful adjustment of the loading and resulting power output of the ART-13 when it is used with an antenna that has low reactance. For months, I just had the variable capacitor setting next to the ART-13 with some wires connecting it to the COND and GND terminals. No problems were encountered with this method but it certainly looked non-military and somewhat dangerous. An aluminum housing was drawn up and we had the local sheet metal shop built four metal enclosures. These would house the air variable capacitors for my two ART-13 transmitters and two of KØDWC's ART-13s. The air variables were fairly large types that I had in the junk box with each having a maximum capacitance of 1000pf and a minimum value of 100pf. About mid-range works very well with the ART-13 when operating on 75M. >>>||
>>> Make sure that the capacitor rotor is connected to both the housing and to the GND terminal on the ART-13. Since the rotor is connected to the capacitor's frame, mounting of the capacitor to the housing accomplishes the ground connection. I used an SO-239 UHF connector mounted on the rear of the housing that also connects to the capacitor frame and the capacitor stator connects to the SO-239 center terminal. A piece of RG-58/U coax with a PL-259 on one end and the other end having the shield connected to the ART-13 GND terminal and the center conductor connected to the ART-13 COND terminal is how the auxiliary capacitor is connected to the ART-13. The bottom cover is a flat piece of aluminum that the sheet metal shop cut for me. The bottom covers mount to 1/4" aluminum square bar that is mounted in the housing. Tapped holes allow mounting the bottom covers and small rubber feet are attached to the bottom plate. I painted my two boxes black wrinkle finish and then used a spare ART-13 knob (D control knob is 0 to 100, 180º scale.) The finished Auxiliary Capacitor box looks very military and like something that should go with the ART-13 transmitter. .
- Today, the ART-13 is one of the "hottest" military transmitters
around. It seems like everyone that has an interest in older gear,
especially military gear, is looking for one or maybe even has one (or
stored somewhere for future
restoration. However, this isn't really a new phenomena,...the ART-13
has been a popular transmitter with hams for the past 50 years. Articles
about converting and using the transmitter go back to the 1960s. As AM
operation was replaced by SSB, the ART-13's popularity did drop but the
resurgence of AM operation during the early 1990s (and the increasing
interest in WWII gear) has brought the ART-13 back to prominence. Though
not intended as a ham transmitter, it is interesting that so many of the
WWII design approaches for this transmitter's circuit are found in later,
Collins gear. The ART-13 has had
a long history with hams as a versatile, potent and good sounding
transmitter and today there are certainly more ART-13s "on the air"
in the ham bands than ever
1. Various ART-13 Manuals - there are several available from BAMA
2. USAF - Radio Mechanics VOL. 1 - Extension Course 3012 - specifically on the ART-13A and the BC-348. Theory, operation, maintenance, course Q&As, informative about post-war uses and maintenance.
3. Electric Radio - N6PY Bill Feldman, article on ART-13 basics. Tells how to perform an initial checkout of an ART-13. Also, a mod on removing the "locking" current off of the Autotune motor when in standby. W6MIT John Svoboda wrote a couple of articles on ART-13 power supply design and on exactly how the loading network operates.
4. Thanks to Mike Everette, W4DSE, for many details on ART-13 history, use, repair and restoration
5. Online - MilSurplus Group, specifics on ART-13 variations by KK5F and WA5CAB
6. Thanks to the many conversations with other ART-13 users and enthusiasts that have provided so much information over the years.
|Like Vintage Military Gear? Want to hear lots of ART-13s
operating "on the air?" On the West Coast, listen in to the Sunday morning "Vintage Military Radio
AM Net" on 3974kc at 8AM Pacific Time.
The Vintage Military Radio AM Net has been in operation for over four years now and has become a particularly successful military radio net in that time. The Sunday morning operating time provides very good, short distance propagation characteristics for Northern Nevada and Northern California. If you have trouble checking into the Southern California-based Military Radio Collector's Group due to its night-time schedule and poor conditions, try the Vintage Military Radio AM Net. You might be surprised at how well 75M morning conditions work for relatively short distance communications. Our net has had regular check-ins from as far away as Eugene, Oregon to the north and San Jose, California to the south.
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