Radio Boulevard
Western Historic Radio Museum

Rebuilding the R-390A Receivers

Brief History - Assessing your Receiver - Disassembly

The Main Frame - The RF Module - The IF Module

The AF Module - The Power Supply Module - The PTO

Front Panel Restoration - Alignment - Performance

Miscellaneous Info on Variants and Accessories,

Restoration logs for:
(2)1967 EAC R-390A Receivers
Collins R-648/ARR-41
Collins R-389/URR Detailed Restoration Log
Recreations of Arvin R-725/URR, ASA R-390A,
Clark AB Black Panel R-390A, USMC OD Panel R-390A

by: Henry Rogers WA7YBS/WHRM

     PART 1 - History, Assessing your Receiver, Main Frame, RF Module, IF Module, Audio Module, Power Supply, PTO


     PART 2 - Front Panel Restoration, Other Details, Contractors List, Receiver Alignment, Expected Performance, R-390A Diversity Operation, Rebuild-Dynamotor R-648/ARR-41, (2) 1967 EAC


      PART 3 - Recreations of Famous R-390A Variants: Arvin Industries R-725, ASA R390A, Black Panel NSA R-390A, USMC Olive Drab front panel R-390A


      PART 4 - R-389 Restoration WARNING! This write-up contains "Extreme ODC" detailed information and it's long, 
R-392 Info,  Other R-390 Variants, Security Dial Cover, CV-979 Cabinet


1967 Arvin Industries R-725

The R-725 is a R-390A that was modified by Arvin Industries to use a special-build Series 500 IF module that was an updated R-390 IF module (no mechanical filters.) Additionally, the R-725 has a ferrous metal shield installed over the PTO and a "hum bucker" addition that allows the PTO and BFO tube heaters to run on DC voltage. For the full story go to Part 3 of this article under "Creating an Arvin Industries R-725 Receiver."


Front Panel Restoration

End-user Panel Repaints - The R-390A specifications state that the front panel is to painted medium gray. The manuals give a specific part number for the paint but it seems the shade of gray did change over the years from contractor to contractor. Also, after fifty+ years on the planet, most of the original paint on the panels will have faded somewhat. When choosing the color for repaint, try to get as close as you can to your receiver's original panel color by having the original paint matched at an professional automotive paint supplier. Use the back of the panel for matching since it's probably the least faded. Only use automotive quality paint for repainting the front panel. Nearly all R-390A panels are found painted gray, however, sometimes the end-users did repaint the front panels totally non-specification colors. Very light gray with black filled nomenclature panels are fairly common. Admiralty Grey, a light green color used on the RACAL RA-17 receivers, has been reportedly used on some R-390A receivers (with black nomenclature.) There were banks of R-390A receivers at Clark Air Base in the Philippines that had black panels that were actually a black grained and anodized finish. Once in a while, olive drab panels turn up, supposedly painted that way by the USMC (see photo right.) At any rate, there's ample evidence that R-390As were painted colors other than gray when the end-users had some reason to do so. Remember, all R-390A receivers left the contractor's facility with gray panels (and that's original) but it can be considered "acceptable" to paint the R-390A panels colors other than gray if there is believable evidence that the color was actually used on a receiver that was operating in a commercial or military capacity. For example, the black panel R-390As were used at Clark AB and there is photographic evidence to prove it.

Silk-screened Panels - All Collins and Motorola R-390A receivers use front panels that have silk-screened nomenclature. This presents a problem if the panel is in rough condition. About the only solution is to look for a decent condition replacement panel. If originality isn't an issue, a silk-screened panel can be replaced with an engraved panel. Be aware though, that most Collins and all of the other contractors used a short serial number tag with the exception of Motorola. The Motorola contracts used a 3" long tag with different locations for the mounting holes. If you're trying to maintain originality with a Motorola contract R-390A, then you're going to have to find another Motorola front panel. (NOTE: Early contract Collins R-390A receivers also use the long 3" data tag.)

Engraved Panels - Repainting an engraved front panel is very easy. Be sure to mask the back of the panel (if you're going to paint it) where the panel mounts to the Main Frame and also a small area by the upper left mounting screw for the Carrier Level meter. Most panels will have nomenclature on the backside of the panel that identifies some of the components. Be sure to use automotive grade paint that is purchased from an automotive paint dealer. This type of paint will have special hardeners that make the paint really durable. Also, professional-quality paint will dry "ultra-thin, hard and flat" which will help make filling the engraving a lot easier. After painting, let the panel dry at least overnight before doing the engraving fill. 

Engraving Fill - I use Artist's Acrylic paint to match the engraving fill paint. If you use pure white it will look way too bright. You should mix a color that is close to that found on manila folders - kind of beige color. Apply the fill paint to only one control nomenclature section at a time. Use a small paint brush and dab the paint into the engraving. Don't try to just paint into the engraving - you have to dab the paint into the engraving to have enough there and, of course, you'll have some paint around the engraving - that's normal. Let the fill paint set for about one minute. You'll now have to remove the excess paint around the area. Use a dampened paper towel folded very flat to remove the excess remaining paint on the panel. You'll have to be careful not to "pull" the fill paint out of the engraved area, so keep the paper towel pieces small and only use them once. You'll have to have several damp paper towel pieces ready as you do each area on the front panel. Also, I've found that if you dampen the paper towel pieces using Glass Plus instead of water the Artist's Acrylic comes off much cleaner. These paper towel pieces should be just damp - not wet! Generally, you'll have to do each engraved nomenclature section twice to get a good fill. Let the first coat dry for about five minutes before applying the second coat. When finished let the panel dry overnight. The next day you can apply carnauba wax to protect the panel and the engraving fill which will enhance the overall panel appearance.

IMPORTANT NOTE: Don't use Windex to dampen the paper towel pieces. Windex contains ammonia which might damage the new panel paint. Glass Plus doesn't contain ammonia but works very well to remove the excess paint without damaging the panel paint.

The Back of the Front Panel - The backside of the front panel has several clamps for holding the harness in place. Also, there is a printed circuit board mounted on the back of the front panel just above the frequency readout bezel. There is a lot of mechanical stress on the various wires when the front panel is lowered so check all of the wires to the pots and switches for any breaks or other problems. Since you have removed the front panel for repainting (or replacement,) then you'll be remounting all of the pots and switches along with the phone jack, dial lock and the zero adjuster. Note also that there is a grounding lug on the upper left (as seen from the front) stud of the CARRIER LEVEL meter. This provides a chassis connection for one of the AGC delay capacitors.

photo above: 1961 R-390A Capehart contract receivers with Olive Drab panels were sometimes the product of a repaint by the USMC
but, in this case, I built-up this recreation of the USMC Capehart R-390A, originally in 2010. It has recently (2022) undergone a complete rebuild for top performance from the "all Capehart" modules (more details in Part 3.)

Mounting the Front Panel to the Main Frame - When mounting the front panel, note that the Dial Lock has to fit over the KC tuning shaft lock-plate. Leave the Dial Lock loosely mounted so it can be rotated to clear the lock-plate. Once the front panel is mounted, you can rotate the Dial Lock into position (the locking grips on each side of the locking plate with the locating tab in the hole one the backside of the front panel) and tighten the mounting nut.

If you have the two large shaft bushings (KC and MC Tuning) and the three small shaft bushings mounted to the front panel you'll find it difficult to guide the shafts thru the bushings because of the harness length. Although you could dismount the harness clamps, it's easier to just plan ahead and slide the rear panel shaft bushing onto the shafts and then mount the front panel to the Main Frame. You'll find with the large openings, it's really easy to guide the front panel over the shafts with the harness clamps tightly mounted. Once the front panel is mounted, then slide the rear bushing forward and slide on the washer and thread on the front bushing.

Once everything is mounted to the front panel and the front panel is fully mounted to the Main Frame (and tightened,) then you can go ahead and adjust the panel shaft bushings for the best feel when rotating the controls.

Front Panel Bearing Adjustment - If you want your R-390A to tune "light and easy" then you're going to have to adjust the front panel feed-thru bearings. These are on the KILOCYCLE and MEGACYCLE tuning shafts.

After a thorough cleaning of the RF module gear box, you probably noticed that the KILOCYCLE tuning was very light and easy to manipulate. As you reinstalled the slug racks, the tuning became slightly more difficult to manipulate but was still very light and easy. When the front panel was installed, all of a sudden the tuning seemed to drag and was noticeably more difficult to manipulate. This is caused by the two panel feed-thru bearings. When the RF module is removed and then reinstalled, it's very slightly, differently oriented and the same goes for the front panel. Only a slight misalignment of the panel bearings will cause a "heavy-feel" to the tuning.

Before the front panel is reinstalled, slide the rear bushing onto each shaft. Fit the front panel into position over the shafts and begin installing the mounting screws. With all of the screws tightened that secure the RF module to the Main Frame and all of the screws tightened that secure the front panel, then slide the rear bushings forward and mount the washer and front bushing nut. Note how the bearings can be moved within the feed-thru mounting hole. This is to allow proper placement of the bushing to act as a guide and bearing for each shaft.

Using a 5/8"open-end wrench, lightly tighten the KILOCYCLE bearing nut being careful to not move the position of the bearing itself. Then try the KILOCYCLE tuning. If the tuning is very light then try to just slightly tighten the bearing a bit more - not too much - the bearings don't have to be mounted "super-tight." If the tuning is still light then the adjustment is fine. Usually, no matter how the bearing is adjusted, there will be a slight increase in the "drag" because of the bearing itself. The adjustment is to achieve the lightest "feel" while still providing support for the shafts.

Do the same procedure for the MEGACYCLE tuning although this tuning is much more difficult anyway since you're moving so many of the slug-racks and there's also a detent about every turn of the shaft. Adjust this bearing for the best "feel." You can also apply a drop of machine oil on the shafts to help lubricate the oil-lite bronze bearing that is inside each of the feed-thru bearings.

The end result will be a KILOCYCLE tuning that is very easy to manipulate and feels great when fine tuning is required.

The three small (.25" shaft) bushings are adjusted in the same manner (ANT TRIM, BANDWIDTH, BFO.)

Use the Correct Lock Washers - Each nut that secures a potentiometer or switch should have a internal tooth lock washer installed. There are five 6-32 flat head phillips screws that mount into the Main Frame bed and into one of the vertical dividers (into pem-nuts) on the underside of the bed. These screws each have a #6 conical external tooth lock washer installed. If you're missing the conical lock washers, they are available from McMaster-Carr (boxes of 100 - they're cheap.) Notice that the three 6-32 flat head phillips head screws that mount the cable clamps have split ring washers mounted on the back side of the clamps (along with nuts.) The eight 10-32 flat-head screws that mount the panel to the main frame vertically will thread into Nylock pem-nuts, so no lock washers are required.

CARRIER LEVEL meter and LINE LEVEL meter - If a R-390A receiver has ever been through a military decommissioning, a surplus house or other "official-type" of handler, both meters will most likely have been removed. There was (is) a concern that the radium-phosphor mix that coated scale and needle represented too much of a long-term radiation source and that was a cause for meter removal and its "proper" disposal. It wasn't necessarily a concern over a single receiver's meter set but, collectively, many receivers being stored together represented a fairly large amount of radium in one area that was going to be radioactive for centuries (radium's half-life is 1600 years.)

Whether or not the radiation level from the two meters on a single receiver is anything to be concerned about is up to the individual user/owner to research and decide. Since the meters are about the same size as an old style radium dial wrist watch a comparison might be interesting. Most data available on radium watch dials seems to indicate that a 1 year exposure by wearing that type of watch was equivalent to ONE coast to coast flight on an jet airliner (24 mSv.)

If you want to get inside one of the original type meters - DON'T EVEN TRY! It's a difficult operation that usually ends up ruining the meter. Special tools are necessary and one should wear protective gloves. When proper original type meters are found (taken from parts sets apparently) they will likely be in "rough" condition. Sometimes it's difficult to remove the outer metal cover, so rather than damage the meter further, just refinish the metal cover in place. It's easy to mask the glass and give the cover a light coat of flat black paint. If there are heavy scratches or gouges, these will have to be removed with either a file or Al-Ox paper followed by a paint job. I've also "touched up" the meter covers and then used 0000 steel wool applied "lightly" to even out the finish. Be sure to use the gaskets (if you have them) between the meter body and the front panel.

If you're contemplating changing the scales to something non-radioactive, this would probably create more of a "radiation problem" since now the scale with the radium is out in the open. How do you dispose of it? It's better to just leave the meter "sealed." Most R-390A owners feel that the meters are safe when installed in the receiver. At a distance of three inches the meter's radiation leakage is not even measurable. It's the phosphor material that "glows" in the phosphor-radium mix with radium providing the energy. However, the phosphor "glow" is depleted fairly rapidly (usually a few decades but it can happen very quickly if the meter scale is exposed to constant sunlight.) Be aware that a non-glowing meter is still radioactive since radium's half-life is several centuries.

A Phosphor-material mix "glows" and Radium provides the energy

Grab Handles - These are made out of stainless steel and can be easily cleaned up with 0000 steel wool and a small brass brush for the washers and the flanges. Wash with Glass Plus before installing.

Dial Cover - This cover, unfortunately, takes a lot of "hits" and as a result is sometimes found dented, scratched or both. Inside the cover is painted with zinc-chromate primer which is bright yellow-green color. Usually the inside is okay but if the cover has dents to be removed, it might need repainting after the body work is finished. Outside the cover is semi-gloss black. Automotive-quality paint should be used for painting the exterior of the cover. NOTE: Minor defects can be touched-up with black lacquer.

Knobs - The knobs also take a beating and many times will need to be restored. First strip the old paint off with a high-quality stripper. Go over the knobs with a wire brush afterwards. Use a high-quality automotive paint in semi-gloss black. Let the paint set overnight. Mix "manila" Artist's Acrylic as described above for front panel nomenclature fill and use the same procedure to add the index line for the knobs. Let this set up for a day and then give the knobs a coat of carnuba wax and install. NOTE: I've found that many times the knobs can be "touched-up" with good results. I use black lacquer paint. I sand the paint chips a little and then dab the lacquer into the chip. As the lacquer dries, it will shrink and become level with the rest of the paint. Inspection of "original" knobs usually will show this method was used in the depots for minor defects.

Tubes - I can't emphasize enough that it's very important that ALL of tubes that are installed in a newly rebuilt R-390A are either NOS or are in "used-tests as new" condition. For the receiver to operate at its full capabilities ALL of the tubes have to be in "as new" condition. As found, nearly ALL R-390As that I've reconditioned had a very weak RF amplifier 6DC6. All three 6C4 oscillator tubes always seem to be very weak and I've found on all R-390A receivers that even if the 6C4 tubes are somewhat over the minimum acceptable, they still will adversely affect performance. The 6C4 tubes should be NOS or test as "used-tests as new" condition. About 25% down from new specs is the actual minimum acceptable (the receiver will function with marginal 6C4 tubes but the range of RF Gain adjustability is greatly reduced and audio modulation on AM-SW BC stations isn't reproduced to its fullest.) The 6AK6 tubes in the AF module also seem to commonly be found in very weak condition. The two 5654/6AK5 tubes also seem to be found weak fairly often. The two rectifier tubes 26Z5 usually test marginal (it's just an emission test for rectifiers.) The 5749/6BA6 tubes seem to last quite a long time (lots of them in the IF module) and the PTO tube is rarely bad. Also, the 5814A/12AU7 tubes (seven used in the receiver) seem to have a long life. BUT, test ALL of the tubes and only use ones that test as "NOS" or "used-tests as new" and definitely replace any weak or marginal tubes. As I've implied, the R-390A will function with marginal tubes and seem to be working okay,...but, with NOS tubes, the reconditioned and aligned R-390A will become a tremendous performer.

Tube Testers - The military TV-7 is a compact and easy to use gm-type tester but it's not the only good tube tester out there. Unfortunately, the TV-7 has become very, very, very expensive these days thanks to audiophiles and tube collector/eBay sellers. There are several other tube testers that work the same way as the TV-7 to measure the tube's mutual conductance. Most dynamic mutual conductance tube testers will be expensive, but maybe just not as expensive as the TV-7. Many of the TV service industry-type of Hickoks do sell for much less than the TV-7 and use exactly the same circuit. Hickok 600, or the 6000, the Hickok 534 and many others were produced for TV repairmen and these are all gm-type testers that sell for much less than a TV-7. Additionally, these testers mentioned have the option for the user to select "English Scale" with "Good-?-Bad" scaling or the user can select the scaling in mutual conductance (usually 3000gm, 6000gm and 15,000gm full scale ranges.) So, the TV-7 isn't the only tube tester around, there are several good options that are much more reasonably priced.

Reducing "High Line" AC using a Line Bucking Transformer - The R-390A was designed to run on 115vac input voltage. Tube heater voltages and the non-regulated B+ voltage is dependent on 115vac being the line voltage used. Today, line voltages are nearly always minimum 120vac and often run up to nearly 125vac. Short term operation, such as testing or alignment, isn't usually affected by "high line" operation. Long term operation however will affect tube life, initial "turn on" surge might be a problem for the 3TF7 and the higher non-regulated B+ can cause an increase in overall heat generated. It's very easy to add an external Line Bucking Transformer to lower the "high line" down closer to the specified input AC voltage. Using a 6.3vac filament transformer (that was designed for 115vac primary voltage) will lower the AC line by about 7vac to 8vac, e.g., lower a 124vac line down to 116-117vac. Our AC line here in Dayton is close to 124vac (123.8vac measured 7/29/22) and Line Bucking with a 6.3vac filament transformer lowers the AC line to 116vac. For receivers I use 6.3vac rated at about 3A minimum transformers and for medium power transmitters I use 6.3vac at about 8A minimum. It's not critical since the VA is only for the drop, not the entire current the equipment draws. You can always use a larger current-rated filament transformer, especially if you want to use it to supply 115vac to a power strip, just be sure to have a primary switch on the bucking transformer. There are lots of easy hook-ups shown on the Internet (search on "line bucking transformer.") Of course, an autotransformer (Variac or Powerstat) could be used just as easily but filament transformers are plentiful and cheap. Variacs are also plentiful, just usually not cheap. Besides, the Variac belongs on the test bench.


Other Details

The Contractor Companies, Contract Numbers and Build-Years for R-390 & R-390A Receivers


1951  -  Collins Radio Co.  -  contract 14214-PH-51 (contract 14214-PH-51 was also used for R-389, R-391 and early R-390A receivers)

1952  -  Motorola  -  contract 26579-PH-52


1954, 1955  - Collins Radio Co.  -  contracts 375-PH-54 or 08719-PH-55  (early R-390As built on 14214-PH-51 contract)

1955, 1956, 1958  -  Motorola  -  contracts 63-PH-54, 14-PH-56, 14385-PH-58

1959, 1960  -  Stewart-Warner  -  contracts 42428-PC-59, 20139-PC-60-A1-51

1960  -  Electronic Assistance Corp.  -  contract 23137-PC-60 (may have been for modules only)

1961  -  Capehart Corp.  -  contract 21582-PC-61

1962  -  Amelco  -  contract 35064-PC-62

1963  -  Teledyne-Imperial  -  contract 37856-PC-63

1963  -  Stewart-Warner  -  contract DA-36-039-SC-81547

1966  -  Communications Systems  -  contract FR-11-022-C-4-26418 (may have been for modules only)

1967  -  Electronic Assistance Corp.  -  contract FR-36-039-N-6-00189

NOTES:  The first few hundred R-390A receivers built by Collins will have long data tags with 14214-PH-51 contract number. Remaining Collins receivers have short data plate with either 375-PH-54 or 08719-PH-55 contract numbers. Amelco was supposedly an alternate name used by Teledyne, as was Imperial. Electronic Assistance Corporation was owned by the same conglomerate that owned Hammarlund in the sixties. It's often reported that Hammarlund owned EAC but the "Hammarlund Connection" for EAC is vague at best.

Ovens - Crystal Oscillator, PTO, Cal. Crystal - There really isn't a need to have these ovens operating. Maybe it was necessary when the receivers were operated by the military and were set up to copy enemy DFSK signals but today's amateur operations don't require that degree of frequency stability and the operation of the ovens increases the heat within the receiver substantially. To turn off the all ovens, look for the switch on the lower right corner of the rear panel. It's marked "ON" and "OFF" and to switch off just align the screwdriver slot of the switch shaft to be inline with "OFF." It's surprising how many R-390s and R-390As will be found with the ovens still operating. It's not necessary and just creates more heat and consumes power unnecessarily. A Note on All-Matching Modules - This is generally an indicator that the receiver has not been used extensively and has not gone through any sort of echelon rebuild. These types of receivers are desirable in one sense since they usually haven't been brutalized by careless technicians. Most enthusiasts consider the "non-matching modules" equipped R-390A to be inferior since it has obviously been worked on in the past. If you intend to use an R-390A "as delivered" then the all-matching modules type gives you a chance this "out-of -the-box" operation might be possible. However, if you intend to rebuild the R-390A before putting it into operation, then the "non-matching modules" type will be a more reasonably priced option. All of the modules are basically the same regardless of which contactor built them. There are minor differences but they are all interchangeable. You will find that the early Collins and Motorola IF modules don't have adjustments on the inputs and outputs of of the mechanical filters unless they've been upgraded. The ECO was issued in mid-1956. It might seem that the early Motorola RF transformers are of a higher quality than the later EAC units (that used American Transformer units.) However, in early RF transformers it's common to find a stuck rotor and stator on the trimmers. This isn't usually found on the later-manufactured RF transformers. These minor issues are just an evolution of production methods. The contactors had to meet a detailed specification when building each module and all modules will perform to spec after a rebuild. Certainly, if you enjoy the rebuilding process, then a "non-matching modules" R-390A will be your most economical route and you won't have to be concerned about disturbing the unit's originality. However, now at 50 years old, even the all-matching 1967 EAC R-390A receivers should be thoroughly checked over before operating.

"Blue Stripers"

When some of the military R-390A receivers were decommissioned, they were sent to a facility located in Portsmouth, Virginia called St. Julian's Creek Annex. At this repository, thousands of derelict R-390 and R-390A receivers were piled one on top of another and stacked side by side on pallets. The receivers typically had their meters removed (due to the radium used on the needles and the scales) and usually the data plates were also removed. Many times the top and bottom covers were already missing. Sometimes receivers were found that still had their meters installed. The story goes that the meters were checked for radiation levels and removed if the reading exceeded a predetermined level. If the radiation level was below the spec then the meter was usually "tagged" with a stick-on paper dot. The final indication that the receiver was "ready to scrap" was to brand it with a "blue stripe" that was generally applied from a spray paint can. Many times, yellow paint was used but the primary use of blue paint has accounted for the nickname - "Blue Striper."

The St. Julian receivers were left out in the weather with no protection whatsoever. The receivers that were in the middle of the vertical stacks generally faired best while the receivers at the top of the pile got all of the rain, snow, sun and dirt and the receivers lower in the pile got all of the debris "run off." The duration of the storage depended on when certain pallets were sold off. At one time, the receivers sold for as little as $37.50 per receiver, taking into account the entire pallet had to be purchased. Usually a pallet contained 12 receivers. Apparently, over the years, R-390As came and went at St. Julian's Creek Annex. Some receivers may have been sold in small lots but the majority were sold by the pallet. It appears that well into the 21st century, R-390A receivers were still being sold from St. Julian's Creek.

St. Julian's Creek Annex - piles of R-390As

It's difficult to tell how deep the pallets go (at least four deep) but they're all double-stacked

Another View of St. Julian's Creek Annex

12 receivers are strapped to each pallet. There are 216 receivers just in the front row of pallets and more behind that

Some of the R-390A receivers sold by Fair Radio Sales in Lima, Ohio were "Blue Stripers" from St. Julian's Creek Annex. The Fair Radio Sales' "Blue Stripers" were the ones that were sold as "needing some work" - maybe a bit of an understatement. Selling price was an incredible $330 in the 1990s. It's generally thought that Fair Radio Sales would put together the "needing some work" R-390As from various condition "parts sets" and "used spares." Consequently, most (if not all) Fair Radio "Blue Stripers" are not true St. Julian's Creek R-390As and probably only have some parts that came from the annex.

The R-390A "Blue Striper" shown above was sold by Fair Radio Sales many years ago and, after its purchase, it sat for many more years in a garage in the San Francisco Bay Area. It was donated to WHRM in 2011 by NU6AM. Note that the panel was repainted a non-original very light grayish-white and the nomenclature has been filled in black. Additionally, this receiver has a Raytheon PTO dated 1977. I would think that this is probably a Raytheon rebuild of a Cosmos PTO. Overall, the condition of this "Blue Striper" is surprising good. Of course, none of the modules match (contractors) which seems to confirm that Fair Radio did "put together" this receiver from parts. What is odd is that they would go through the trouble to assure that relatively good condition modules were provided and then use a "Blue Striper" front panel.

Update 2013: Unfortunately, like a lot of receivers in the condition that this "Blue Striper" was in, this one has gone on to become a source of parts to restore other R-390A receivers that have faired better. The RF deck has gone into a 1962 Teledyne R-390A, the IF module has a bad 4kc mechanical filter but provided several parts in the restoration of a Capehart IF module*. The PTO was going into a 1961 Capehart but its cosmetic condition is "challenged." The ON/OFF microswitch went to repair an Amelco R-390A. It's unfortunate but "parts sets" are needed for restorations and also as a source of parts to keep other R-390A receivers in "top condition" so they can be operated and appreciated for the impressive performance they can provide the user/owner.

*In 2022, I rebuilt a Capehart IF module and used the 8kc and 16kc mechanical filters, the CL ADJ pot, the IF Gain pot and Z503 from this "Blue Striper's" IF module (it's really a wreck now.) The "Blue Striper Main Frame also was harvested for several mechanical parts for the Capehart OD panel rebuild in 2022. 


R-390A Receiver Alignment - Miscellaneous Info

Initial Power-up after Rebuild  You should have the R-390A receiving stations on all bands with power on. You can turn on the CAL and the BFO. Then tune to a 100kc calibration signal. Now rotate the MC knob through each of the bands listening for the calibration signal. Normally, you'll hear the CAL signal on every band although it will be at various tone-frequencies depending on each band's particular alignment at this time. You should hear the signal on every band though. This will assure you that everything is basically working and the receiver is responding to an input signal on each tuning range.

Things to do Before Proceeding to the Fixed-IF, Variable-IF and RF Alignments - you should first do your PTO end-point error correction, if necessary (it will be.) Be sure that the Calibration Oscillator is set correctly and the Veeder-Root counter is in sync with the PTO (you should have checked both before doing the EPE adjustment.) Also, check the Crystal Oscillator output at E-210 and be sure the voltage there is between -3.5vdc and -8.0vdc on the 8mc to 31mc tuning ranges. The voltage should appear when the MEGACYCLE knob is on its detent for each band. You don't have to check the .5mc to 7mc bands because these crystals and associated oscillator circuits are both fundamentally and harmonically operated and also work in either a double or triple conversion scheme. They were actually checked in the higher ranges. Be sure your DIAL ZERO is mechanically centered within its approximately one-sixth turn of the KILOCYCLE tuning when calibrated to XX.000 on the Veeder-Root counter.

Error in Army TM 11-5820-358-35 and more - Field Depot and Maintenance Manual for the R-390A from December 1961. Alignment instructions, page 116, paragraph 76b (2) indicates that URM-25 Signal Generator should be tuned to 18.75mc. Actually, the correct frequency is 18.25mc. This error was very obvious to technicians doing the alignment and is very well known. Interestingly, the earlier TM 11-856A Technical Manual for the R-390A has the correct 18.25mc information, so this later error was probably a typo that wasn't caught in proof-reading. There are many conflicts in the Army TM schematics due to the reluctance of the Army to change the schematic. Instead "NOTE" is placed on the schematic that should guide you to a list of upgrades that changed the schematic or component value. Just be aware that if you're troubleshooting to the component level to double-check if a circuit value is in conflict with what is shown on the schematic.

How to do the Balanced Input Alignment - Make up a test resistance that consists of two 68 ohm 1/2 watt carbon resistors in series. Each separate leg of the resistors will push into to each terminal of the Balanced Input Twin-ax connector. The junction of the resistors will be connected to the signal generator. When performing the alignment of the RF stages first adjust the Balance trimmer on the the RF transformer for the minimum voltage on the DIODE LOAD as read on an (analog) VTVM. The Balance adjustment will not reduce the DIODE LOAD voltage to zero - you're setting the Balance trimmer for the minimum voltage. Be sure the ANT TRIM is set to 0. With the minimum voltage set, now proceed with the RF adjustments for that section of the receiver. Recheck the Balance trimmer adjustment after the particular RF section has been aligned. The Balance should still be close but will probably need just a slight adjustment for minimum voltage at the DIODE LOAD. Recheck the RF alignments - but there should be no significant change and just a slight "tweak" should be all that's required.

Does it Really Matter - Balanced or Unbalanced Input? - If you do the Balanced Input alignment, then the answer is yes. Correctly aligned you might see an improvement if you are using an adapter that grounds one side of the two terminals and connects an unbalanced antenna (that is matched for the received frequency) to the other terminal. This method runs the signal through a set of tuned coils before going to the RF amplifier stage. If you haven't performed the balanced alignment then it's very possible that a reduced signal level may be experienced with this method of connecting the antenna. In this case, connect your antenna to the Unbalanced input (but, eventually, you'll want to do the Balanced Input alignment.) Originally, the Balanced Input was for dipole antennas that used a balanced feed line in the 100 Z ohm range utilizing the "twin-ax" type coaxial cable. Nowadays, hardly anyone runs a balanced antenna directly since most transmitters operate into unbalanced loads. Additionally, the "twin-ax" type cable has a significant db loss per foot. If you're using a tuned antenna with antenna coupler, you might find that the Unbalanced input works better. This may also be the case if you're using a vertical antenna directly fed with coax. Go ahead and do the balanced alignment and then test both Balanced and Unbalanced inputs to see which nets the best results with your particular antenna.

Stagger Tune the IF or Peak Adjustment of the IF? - Stagger tuning will give the IF bandwidth the maximum flat top possible with the mechanical filter selected. Early receivers were "peak" tuned for maximum response and may give a frequency bandwidth somewhat less than the mechanical filter bandwidth. Stagger tuning was used on the later IF modules and does give a better response in the receiver that is generally flat out to the limits of the mechanical filter's bandwidth. You can align early IF modules using the Stagger Tune method. Be sure to check the IF transformers to verify that the Q-spoiler resistors are present. Some IF transformers were modified by clipping out the Q-spoilers to have more IF gain but this also narrows the bandwidth. The Q-spoilers should be installed and connected for the best bandwidth. Updates to TM11-856A have the later procedure for stagger-tuned IF alignment, as does TM11-5820-358-35, or it can also be accessed from many sources on the Internet.

IF Cans without the Alignment Hole - Early production IF modules will have shields over the IF transformers that don't have a hole for alignment. This was to assure that the receiver's IF alignment wasn't tampered with in the field. When the receiver went back for repair or alignment the technicians had a set of covers with holes that were installed for the alignment and when the alignment was finished then the "non-hole" originals were re-installed. If you can't locate an extra set of IF cans then it will be necessary to drill an access hole for alignment. All later IF shields had the hole anyway and many early ones are found nowadays with the hole already drilled since the TM directs the technician to drill a hole for alignment purposes.

Slug and Trimmer Adjustments - One caution on adjusting the slugs and trimmers for the RF alignment. First set the Veeder-Root counter on the R-390A to the specified frequency. Then set the RF Signal Generator to its specified frequency. You'll notice that by "rocking" the Signal Generator frequency that there is a "peak" output on the Diode Load that is very slightly different from the Veeder-Root counter setting. Be sure to use the "peak" Diode Load voltage set by the Signal Generator frequency adjustment. Once you've set the signal generator to have the peak Diode Load voltage, then adjust the proper slugs or trimmers for further maximizing of the Diode Load voltage. Remember, the slug adjustments don't affect the receiver's frequency readout accuracy. That's a function of the PTO accuracy and the Crystal Oscillator. Always set for the "peak" response by "rocking" the RF Signal Generator and then adjust that band's slugs and trimmers for maximum output on the Diode Load.

What to do about early IF modules without the Mechanical Filter trimmer caps? - The trimmers were added with the 1956 contract R-390A receivers. The earlier IF modules will have fixed-value 110pf mica capacitors to tune the input and output of each mechanical filter. When checking these earlier IF modules, it will be necessary to measure the output  and see whether or not each of the Bandwidth positions (16kc, 8kc, 4kc and 2kc) are more or less equal for a constant, known-value input signal. The easiest way is to use the CAL and tune to zero beat and watch the CARRIER LEVEL meter. For instance, if 16kc and 8kc measure 50db on the meter but 4kc measures 40db and 2kc measures 50db, then something is wrong with the 4kc mechanical filter. When doing this test, you'll notice that the fixed tuned mechanical filters are not equal but are usually fairly close - within 5db of each other. If the four filters are not close in their equal response it will be necessary to reselect the tuning capacitors on the filter that is different (hopefully, it's only one filter that has been affected.)  Try to select capacitors so that each Bandwidth position results in a fairly equal output in all four Bandwidths (mechanical filter derived bandwidths, that is.)

Make up an adjustable trimmer that has a range of about 80pf up to around 130pf. Remove the cover from the mechanical filters on top of the IF module and then remove the 110pf fixed capacitor on the particular mechanical filter. Now "tack solder" the trimmer in its place. Power-up the receiver and select the bandwidth for the particular mechanical filter and adjust the trimmer for maximum reading on the CARRIER LEVEL meter. Remove the trimmer and measure the capacitance with a digital capacitance meter. Install a silver mica capacitor of that value to the mechanical filter. This may be enough to get the mechanical filter tuned enough for equal response but it usually isn't.   >>>

>>>  To do the capacitance selection for the mechanical filter output will require accessing the underside of the IF module. You can loosen the BANDWIDTH and BFO knob-shafts and pull them forward. Then undo the IF OUTPUT coax cable and loosen the three captive screws. The IF module can now be lifted in the front and placed in a vertical position. Use rubber spacers to "prop up" the IF module. Remove the fixed silver mica on the particular mechanical filter and "tack solder" the adjustable trimmer. Power-up the receiver and switch the BANDWIDTH control for the particular mechanical filter and adjust the trimmer for maximum reading on the CARRIER LEVEL meter. Remove the trimmer and measure its capacitance and install that value silver mica on the mechanical filter. Replace the IF module and the knob-shafts and give the receiver a final test to see how the new tuning compares. Hopefully you'll be able to retune the mechanical filter to be within 5db of the other mechanical filters. Needless to say, the 1956 upgrade that added adjustable trimmers to all of the mechanical filters made everything a lot easier.

NOTE: Most handheld digital capacitance meters aren't even close for accuracy when measuring pico-farads. Not to mention that, at the pf scale, the test meter leads will also add significant C (some meters have a zero adjust but still the accuracy is limited.) It makes this sort of fixed-value tuning difficult to do accurately. Unless the input/output fixed C is way off, it's probably better to just leave the MF tuning "as-is." The spec was within 5db of the other MFs. It would have to be over 10db before I'd try this method of retuning the MF. And,...actually an easier approach is to install the MWO for adjustable trimmers - well, actually just use an IF deck that already has the MWO, then just test and install. Keep the original IF module around just in case for some reason you want an "all original modules" R-390A.


Expected Performance

I've used many R-390A receivers in my various ham radio and vintage military radio station set-ups over a period of many years. My first R-390A was a 1959 Stewart-Warner version that worked pretty well "as-is" when I got it from a ham swap meet in 1991. I used it with an Eldico SSB-100F transmitter I had and performance was great. A few years later I obtained an excellent EAC version from 1967 but I sold it to buy a 1951 contract Collins R-390 installed in a CY-979 cabinet. I still own and use the R-390 on a regular basis. I sold the 1959 Stewart-Warner after obtaining a 1955 Collins R-390A. This Collins R-390A was given to me as payment for repairing and rebuilding a Motorola R-390 for a fellow ham. Eventually, I "wheeled and dealed" my way into a 1956 Motorola R-390A, a 1961 Capehart R-390A and a "Blue Striper" survivor from St. Julian's Creek Annex. In 2016, a bargain-priced 1967 EAC was purchased. It needed a little TLC and turned into a great receiver. Another '67 EAC showed up at a bargain price in 2017. In 2019, I traded some BC gear to a fellow collector for his entire stock of R-390A parts sets and modules. From that collection I was able to recreate an original Arvin Industries R-725 (R-390A with R-390 IF deck.) I've used all of these receivers except the "Blue Striper" at one time or another, both as an SWL receiver or as a Station receiver.

Here's what I like about the R-390A,...

1. If you absolutely must know exactly where in the electromagnetic spectrum you are listening, the R-390A and its family are the most frequency-accurate readout available in vacuum tube receivers. It's easy to achieve 1/2 kc accuracy or better. The mechanical-digital readout eliminates the vague interpretations of reading analog dials.

2. If you think you're going to be bothered by QRM, remember the R-390A was designed to intercept radio signals from the USSR, China, Cuba, East Germany and other Communist countries and to be able to successfully copy those signals through any kind of interference whether natural or man-made. The R-390A also provided reliable communications, including mobile RTTY, despite jamming efforts from some of our Cold War adversaries. The receiver can cope with just about any type of amateur interference since it was designed to work through "professional-level" QRM.

3. When the R-390A is rebuilt and correctly aligned it is very competitive as far as sensitivity is concerned. Are there more sensitive receivers? Of course, but sensitivity isn't all that's required to successfully copy weak signals. Nowadays, the ability of a receiver to function well in a noisy EMI environment is far more important than an "under a microvolt sensitivity" spec. After all, when your local EMI noise floor is a constant S9, what good is .25uv sensitivity? When all the available controls are taken into account along with the mechanical filter selectivity (and the user is very familiar with the operation and capabilities of the receiver) the R-390A is almost unbeatable as a station receiver.

4. Stability is the best in vacuum tube designs. Drift is non-existent.

5. You have two individual audio outputs on an R-390A. The LOCAL AUDIO is normally used to drive a 600Z ohm speaker set-up but you can also use the LINE AUDIO for the same thing - simultaneously! The LINE AUDIO was normally used to drive data devices like RTTY TUs, etc., but there's no reason it can't drive any 600Z load - like another speaker. I've set up a speaker in one room run by the LINE AUDIO and a second speaker in another room run by the LOCAL AUDIO. Independent audio levels in separate rooms. Really neat.   OR,...if you just want to utilize the LINE LEVEL meter to show a response to the audio component of the signal then install a 680 ohm 1/2W resistor across the LINE AUDIO terminals. You can now turn on the LINE GAIN and select the LINE METER scaling and the LINE METER will respond to the audio component of the received signal.

6. Everything about the R-390A's construction is "heavy-duty" and its use metal knobs imparts a massive "feel" to the receiver's operation. The R-390A has a certain impressive presence that attracts the attention of ham shack visitors. This seems to be true whether the visitor is familiar with the R-390A receivers or not. 

The following might be concerns for some users,...

1. On SSB and the Meters - Although there were a couple of military SSB adaptors , the CV-591A (aka MSR-1 or MSR-4) and the CV-157, available and several modifications have been published and other add-on devices available for demodulating SSB produced, none of these are necessary for receiving undistorted SSB signals. Unfortunately, many new R-390A owners have only used modern equipment (with SSB Product Detectors) before going to the R-390A which only has a simple Envelope Detector. They expect the R-390A to be adjusted for SSB reception just like their modern receiver - RF GAIN at maximum with the AVC (AGC on the R-390A) on and volume level set by the AF GAIN (LOCAL GAIN on the R-390A.) The R-390A can't be operated like that when receiving CW or SSB. Before product detectors came along it was standard procedure when receiving CW or SSB to reduce the RF GAIN and advance the LOCAL GAIN (AF GAIN) so that the proper ratio of incoming signal to BFO injection could properly demodulate either CW or SSB. AGC was usually turned off but it depended on the receiver. With the R-390A, AGC can be left ON to limit the maximum response, if desired. If the R-390A's BFO is properly set-up, its position allows selecting either upper or lower sideband. Now, you do lose the function of the CARRIER LEVEL meter in this method of reception but who cares? The CARRIER LEVEL meter measures DB over 1uV and its accuracy depends on the RF GAIN setting. If you were planning to use the CARRIER LEVEL meter for CW or SSB signal reports, most stations wouldn't even know what you're talking about when your report was so many "db over 1uV." It's all a relative measurement anyway, dependent on the frequency and conditions. It's better to operate the R-390A as a standard pre-product detector receiver for CW and SSB and just give your contacts an estimated R-S-T report.

2. More on the subject of SSB reception and Modifications - The CV-591A family of SSB adapters were built by The Technical Materiel Corporation. These adapters work from the IF output, therefore you lose the Noise Limiter function, the 800 cycle filter function and the dual audio section of the R-390A receiver if you utilize only the audio output section of the CV-591A. Now, if you happen to have an extra speaker, you can connect one to the CV-591A output (8.0Z or 600Z) and the other one to the R-390A's LOCAL AUDIO (600Z only.) If you want to do SSB or CW you can use the CV-591A and its speaker. If you want to do AM, then use the R-390A's LOCAL AUDIO and speaker. The CV-591 will provide excellent, distortion-free SSB reproduction and they are well-worth using. The only disadvantage is the price that the CV-591A is fetching today, sometimes selling for more than the R-390A receiver. 

On modifications to enhance SSB reception,...most of the mods that have been published do not improve the receiver's overall performance. Most modifications on any piece of vintage radio equipment will enhance performance for one area at the expense of overall performance. Besides, modifying a vintage receiver to make it operate like a "modern" piece of equipment seems to go against the whole idea of collecting, restoring, operating and preserving these classics in the first place. You're better off to learn how to use the R-390A properly and when you do, you'll find that modifications are not necessary for great performance in all conditions and in all modes.

3. On Audio Quality - Audio reproduction is not as bad as a lot of "BC-Quality AMers" complain it is. The mechanical filters provide a specific, very steep-sided bandwidth but some AM op-listeners are used to the "bell curve" that many early vacuum tube receivers had with only two fairly broad-tuned IF amplifiers. "Ringing" or a "hollow sound" were the usual complaints about the mechanical filter bandwidth. If you change the LOCAL AUDIO coupling capacitors to .022uf and then use a high quality 600Z transformer with a large speaker in a good enclosure, the audio sounds very nice, especially in the 8KC bandwidth (which is really close to 11KC) on AM with marginal signals or 16KC with a really great signal level (AM or SW Broadcast but it's hard to find quality program material being broadcast.) You'll have to do the same thing to the LINE AUDIO if you want to run dual audio lines to two separate speakers. However, if you're really into high-fidelity, then you can take the signal from the DIODE LOAD and run it through a shielded cable to a high-fidelity audio amplifier that's connected to a large hi-fi type speaker system. At 16kc bandwidth, AM signals will sound incredible. As with the SSB adapters though, you'll lose the NOISE LIMITER and 800 cycle audio filter functions with this "hook-up" unless you provide a separate speaker on the LOCAL AUDIO line (just in case you want to do CW.) For most users though, especially if you're using typical communications loudspeakers, the stock audio sounds pretty good and the original .01uf coupling caps are fine. I've only substituted the .022uf on a couple of R-390A receivers (and that was done years ago) and it's difficult to tell the difference between those receivers and the ones with stock coupling caps.

Here are some disadvantages to using the R-390A  -  minor stuff, really,...

Break In Operation - The R-390A "Break In" function requires using a T-R relay with Normally Open (NO) contacts that change to Normally Closed (NC) when in transmit. This function operates the R-390A Break In relay and the R-390A Antenna Relays. The Break In function of the R-390A is opposite that of a typical receiver Stand By function that will require the T-R relay to provide a NC state for receive and NO for transmit. Most T-R relays, like the Dow-Key type, will usually provide a set of DPDT auxiliary contacts that allow connecting the R-390A Break In to one of the NO set of contacts. Most vintage military transmitters will have internal T-R relays that provide receiver antenna switching and also NO and NC contacts on the sending relay to control the receiver standby.

The Weight Issue - No doubt, the R-390A is a heavy receiver weighing in at close to 85 lbs. Here's a hint for when you have to move the receiver. Remove the Power Supply module and the AF module. These two modules will reduce the weight by close to 20 lbs. With the covers off and the two modules out the receiver weighs about 65 lbs - much easier to move. Of course, you do have to get the receiver to the work bench to remove the covers and modules (use a roll-cart.) This hint is really for moving the receiver longer distances, like to another room, ESPECIALLY when the moving involves going up or down stairs.

Cabinets - If you want the R-390A to be mounted in a cabinet you have two choices. First, is to find the proper CY-979 (or CY-979A) aluminum cabinet. This is a high-quality, military cabinet that is designed for the R-390-family of receivers. They are expensive. Originals were built from the early fifties up well-into the sixties. In the 1990s, an ad in Electric Radio offered CY-979 cabinets for about $150-$200. These cabinets were restored by W5MC and ink-stamped on the interior with an ID. There is some confusion on these restored cabinets as it wasn't clear in the ad if these cabinets were rebuilt old ones or new recreations. It doesn't seem likely that someone could have built a CY-979A complete with shocks and skids and then sell it for so little. But, since any original contractor ID was removed in the restoration process, the only ID is the ink-stamp inside which usually has a date with it (from the 1990s.) I've only seen one of these W5MC CV-979A cabinets and it was exactly like the original, with the screens inside the louvers, proper shocks and skids, etc. I would have to conclude that these W5MC cabinets are "restored" originals. If you are going for the CY-979 cabinet and you're willing to pay a high price be sure that the one you decide on has the shock mounts and the skids. It's fairly common to find CY-979 cabinets with the shocks and skids removed. These cabinets are incomplete and should be priced accordingly. For more details on the differences between the CY-979 and the CY-979A, go to the section on these cabinets at the bottom of the page in Part 4 of this write-up. Other than the CY-979, any other cabinet that is for 10.5" by 19" panels with a depth of 15" will also work. Several sources sell a new Hammond cabinet of this size. Although advertised as a "R-390A Cabinet" it really is just a cabinet in which the R-390A will fit. Price is several times less expensive than the CY-979.

Quick Check for Prospective R-390A Purchases -  The following "Quick Test" assumes you are at the seller's QTH and have AC power available. The test doesn't require anything other than the powered-up R-390A and can be used for any R-390 or R-390A receiver that you are interested in purchasing. Hopefully the seller will allow this easy test since you don't need an antenna (a common excuse from sellers for not providing information is lack of an antenna.) Though a loudspeaker connected to LOCAL AUDIO would help, you don't actually need a loudspeaker but make sure both LOCAL and LINE gain controls are set to "0" if a speaker (600Z ohm load) isn't connected. If you bring your own 600Z ohm speaker, if the seller is agreeable, connect it to the receiver LOCAL AUDIO terminals.

Put on the CAL and the BFO, set the KC to xx.500 kc and rotate the MC change thru all bands to hear if the CAL oscillator is received on all bands. Turn off the BFO, make sure the RF Gain is fully advanced, AGC is selected and then, watching how much the CAL oscillator shows on the Carrier Level meter, run thru the bands again. The meter level should read over 40db. 50db is more likely if everything is aligned. Be sure to check all bands for CAL Carrier Level. With the CAL still on, check the EPE on any band. Be sure to also check the linearity every 10kc. That's an easy test that shows a lot. Recent alignment should have no more than 0.5kc EPE and an unknown PTO might have up to 4kc EPE but should still be linear with just a slight change each 10kc increment. These two tests are easy to perform and tell you a lot of info. If both tests look good, the receiver is probably in good shape. This applies to any R-390A that you want to perform a "quick check" to.

Since the CAL oscillator is practically connected to the Antenna Input, it serves as a onboard signal generator. If you hear the CAL oscillator when tuning through the 100kc markers on all bands (if you have a speaker connected,) then most of the receiver is working well enough to receive a strong signal. The reading on the Carrier Level meter will show generally how sensitive and in alignment the receiver is. Most rebuilt and aligned R-390As will show 50db+ on the meter at around 10mc. Check around 5mc and the meter should read the same or slightly higher. Check around 15mc and the meter will probably read less but still be around 40db. The EPE check just tells you if the receiver has been recently aligned by someone who is thorough and did do the EPE adjustment. EPE < 1kc, recent alignment. EPE > 4kc, typical of "as found" PTO.

You never know how a seller is going to react to this testing, so before doing any testing, be sure to describe what you want to do, what you're going to be looking for and why. Most honest sellers would welcome more detailed information on what they're selling. However, many sellers will react to this testing as a "haggling method" and become suspicious of your motives. If the seller has technical ability, they'll usually understand the testing and the results. If the seller doesn't even know what the R-390A is other than something to sell,...well, not much can be done in that situation. Actually, when dealing with non-technoid sellers, you're trying to access the condition of the R-390A for your own motives and from that information judge if it's priced accordingly. If it's priced fairly for its condition, then buy it. If it's not fairly priced,....well, all of the haggling efforts are usually a waste of time when dealing with the non-technical type of seller.


Dual Space Diversity Operation with the R-390A Receivers

If you're lucky enough to own two R-390A receivers and have room for widely separated antennas, you can easily set up the pair to operate in Dual Space Diversity. Good separation of the antennas would be at least one wavelength at the frequency of operation but usable diversity effect can usually be obtained with closer spacing if necessary. Space Diversity assumes you will be using two similarly polarized antenna and are relying only on the phase differences of the radio wave based on the spacing of the antennas. You can also try "Polar Diversity" which relies on a vertical antenna for one receiver and a horizontal antenna for the second receiver. Polar Diversity doesn't require that the two antennas be separated by great distances and assumes that there will be a benefit from the reception of two different polarizations of the incoming radio wave. This assumes that some splitting and rotation of the radio wave will occur as it propagates through the ionosphere and is returned to earth. Generally, space diversity helps with fading signals and polar diversity helps with phase distortion due to wave rotation. 

With either method of Dual Diversity reception, the receiver set-up is the same. You will be connecting the DIODE LOAD from each receiver together. The receiver that you plan on operating as the "master" will have to have the DIODE LOAD terminals jumped while the "slave" receiver doesn't have the terminals jumped. The "slave" receiver is only operating to the detector stage and its audio output is not used. You can connect 500 ohm resistors across the LINE AUDIO and the LOCAL AUDIO on the "slave" receiver. You will also have to install the jumps to connect AGC DIV terminals together on each receiver. You will also have a wire connecting the AGC DIV from each receiver together. A speaker on the LOCAL AUDIO is only required on the "master" receiver.  To listen to just the "slave" receiver, turn the RF GAIN on the "master" receiver to 0 and what you hear thru its speaker is the "slave" receiver. Also, if you want to listen to just the "master" receiver, turn the "slave" receiver's RF GAIN to 0 and what you hear thru the speaker is the "master" receiver only. With both receivers operating and connected to their respective antennas, tune in a strong shortwave broadcast signal. Have both receivers' RF GAIN set to about 8. Don't set the RF GAIN on either receiver to "full on" (10) or each receiver will "fight" the other one for control of the AGC line. By alternately reducing the RF GAIN of each receiver to 0 you should be able to end up with both receivers tuned exactly to the signal. Once the SW BC signal is tuned in on each receiver you will need to "balance" the RF GAINs. Slowly increase the RF GAIN on the each receiver alternately to the point where you see the CARRIER LEVEL meter showing some response. Adjust the RF GAIN on each receiver until you have the highest CARRIER LEVEL readings on each receiver without one receiver or the other "overloading" the AGC line. When "overloading" occurs the CARRIER LEVEL meter on one receiver will drop much lower in its reading and with a reduction in the RF GAIN of the other receiver you'll see the meter reading jump back up. By "balancing the receivers" you get the best diversity response and the best sensitivity. You will note that the two receiver's CARRIER LEVEL meters will react differently since each receiver is responding to a phase difference in the radio wave based on the separation of the antennas. You should see deep fades that cause one CL meter dip while the other receiver's meter remains steady. You should also see a reduction in phase distortion if you are using the polar diversity set up.

Remember, you can only use AM reception on this type of Dual Diversity. That's because CW or SSB reception requires the BFO to be in operation and the BFO dominates the detectors and spoils the diversity effect. For RTTY reception special TUs were used like the CV-116 that was designed for diversity RTTY. Diversity CW reception required Tone Keyers.

So, give Dual Diversity reception a try if you can. It's interesting and sometimes beneficial to copy. 

photo above
: A Dual Diversity set-up with the 1956 Motorola on the bottom and the 1955 Collins on top. Both receivers are fully rebuilt (including recapping) and both are fully aligned. Though the speaker looks like a Hallicrafters PM-23, it isn't. It's a homemade wooden cabinet that houses an 8" Jensen speaker and the louvers are made of aluminum. The cabinet is painted gray wrinkle finish.


R-390A Receivers and Variations
Rebuilding, Refurbishing and Recreating Projects


Dynamotor Retrofit for the R-648/ARR-41

The R-648/ARR-41 is the so-called "Airborne R-390A." Certainly the nickname comes from the intended use of this Collins-design/build along with its many similarities of construction and operation to this receiver's "bigger brother," the R-390A. However, Collins' engineers borrowed a lot of the circuitry from the 51J Series of receivers. Since the R-648 was destined to be used in aircraft, it had to be light-weight. Rather than the 80 pound, hefty-weight of a R-390A, the R-648 weighs-in at about 30 pounds. To achieve this lighter weight package, the receiver is much smaller, with reduced-size mechanics and components. Of course, most of the R-390A features and circuits are not even present. Still, with 17 tubes that provide two RF amplifiers, three 500kc fixed-frequency IF amplifiers, frequency coverage from 190kc to 550kc and from 2mc to 25mc, two mechanical filters (9.4kc and 1.4kc - the 9.4kc MF was later changed to 6.0kc) and a mechanical digital frequency dial, the R-648 does have a few "R-390A" features. The circuit conversion methods were borrowed from the 51J/R-388 by using a dual variable IF and fewer crystals in the Crystal Oscillator along with the 500kc IF. Double conversion is used on all frequency ranges except for the 2-3mc band and the 3-4mc band where single conversion is used. Audio output has three stages and was designed for a headset of 300Z ohms or greater. Typical antenna input Z is 50 ohms.

photo right:  R-648/ARR-41 SN: 816 COL from 1957 contract NOas57-438. The shock mount is not original but is homemade. It does have the correct type metal and cushion shock feet installed although they can't be seen because of the front piece of the mount.   

photo above: Top of the chassis showing the various plug-in modules.

The R-648 operated on +28vdc battery-charger buss available on the aircraft. The +28vdc buss supplied the series-parallel connected tube heaters, the dial lamps and also operated the "on-board" dynamotor. The dynamotor supplied +250vdc at 100mA. A regulator tube type 0A2 was used to also provide +150vdc from the +250vdc. A divider network also provided +31vdc for the AVC bias. Unfortunately, like a lot of the dynamotor-operated military gear, many R-648 receivers have been converted to operate on an AC power supply. Some modifications were well-designed and their incorporation into the receiver was accomplished with minimal modification to the receiver while still providing the necessary voltages. Most AC power supplies utilize the original dynamotor module chassis since this then has all of the circuitry for the 0A2 regulator and the divider network for the +31vdc. Usually two power supplies and two transformers are necessary, one for the +250vdc supply and one for +24vdc for the tube heaters. Some better conversions utilize a DC-DC converter to provide the +250vdc and then the receiver is operated on +24vdc input. In essence, providing a solid-state substitute for the dynamotor only. If you don't have the original dynamotor, this is probably the best solution to keeping the R-648 as original as possible.

Shown to the left is the top chassis of the R-648. Directly behind the front panel is the gearbox and the RF module containing all of the RF transformers, VIF transformers, slugs and slug racks. To the right of the RF module is the PTO. To the right of the PTO is the dynamotor module that provides +250vdc, +150vdc (via the 0A2 regulator tube) and +31vdc. Behind the Dynamotor is the Audio and RF Spectrum Oscillator modules. To their left is the Crystal Oscillator module and to its left is the IF module with the two mechanical filters. The front panel also "plugs in" and has enough wiring to be considered another module. The front panel hinges down for easy access.

photo above: The NARF NORVA sticker on the front panel. There is also another NARF NORVA sticker on the chassis.

As to the R-648 operation, the GAIN control operates RF gain when in CW and AF gain when in AM. The Sensitivity is a screwdriver adjusted pot accessible on the front panel behind a "toilet seat" cover. The overall Audio Gain is a screwdriver adjusted pot accessible on the rear panel. The audio output impedance works well with 600Z ohm loads and a loudspeaker with a 600Z ohm matching transformer will have plenty of volume. The manual doesn't specifically give an output impedance only stating that the load should not be less than 300Z ohms.

Selectivity is controlled by two mechanical filters. On early versions, the AM filter is 9.4kc. This was later changed to 6.0kc to improve selectivity in the Voice mode. CW selectivity used a 1.4kc mechanical filter. The selectivity is automatically switched between the two mechanical filters when either VOICE or CW is selected by the EMISSION switch. The "SHP" positions are "sharp" selectivity and add an audio filter to reduce bandwidth to improve copy in noisy conditions.

Although the R-648 is called "The Airborne R-390A," don't expect the receiver to have the robust construction or all of the capabilities of its namesake. The R-648 has ample sensitivity, adequate selectivity in most circumstances, a minimal amount of knobs to adjust and lots of volume available if the proper load impedance is supplied. Its light-weight and small size make it easy to find a place for on the bench. 

NARF NORVA - NARF stands for "Naval Air Rework Facility" and NORVA stands for "Norfolk, Virginia." These stickers showed the receiver rework dates. The first quarter of 1975 is marked on this tag. Also note "IRAN." This isn't the country Iran, it's an acronym for the facility's process of "Inspect, Repair As Needed."

Dynamotor Retrofit - In 2017, I purchased an original R-648 dynamotor. It was just the dynamotor, not the entire power supply chassis. When looking at the AC power supply that had been built and installed in the R-648, it was apparent that it was built on the original dynamotor/power supply chassis. Even the regulator tube circuitry and many other original parts were still within the chassis. I purchased the dynamotor with the idea that I could rebuild the AC power supply back into the original dynamotor configuration.

This particular R-648 had been severely "hamstered" in that the original front panel power box connector was removed and a Jones plug installed to allow a 120vac power cord to be plugged-in the front panel. Much of the "behind the panel" wiring had been "hacked" to incorporate this modification. Luckily, I was able to obtain a good condition, original R-648 front panel from Fair Radio. This panel was complete but had a slight bend that needed to be straightened before it fit correctly. 

Unfortunately, the AC power supply couldn't be wired into the front panel unless I wanted to incorporate some modifications and that was what I was trying to avoid. The only solution was to rebuild the power supply into the "original dynamotor" unit and run the R-648 on +27vdc, as originally done.

I removed the power supply module from the R-648 and removed all of the parts that were not original. This left the chassis, the 0A2 regulator, the 11 pin connector, a choke, a couple of resistors and a couple of ground lugs. The photo right shows the R-648 when it had the homebrew AC power supply installed.

Servicing the Dynamotor - Most dynamotors found today haven't had anything done to them in several decades. The R-648 dynamotor only needed a servicing. This consists of removing the end-bells to access the brushes, the commutators and the bearings. I mark the brushes for location and orientation so when reinstalled their fit to the commutator is correct. With the brushes removed, I use a small piece of 400 grit Al-Ox paper to clean the commutator surfaces. I wash the commutators afterward with denatured alcohol. I run some light-weight oil through the bearing to clean out the old grease. I then work new grease into the bearings. These bearing are somewhat "sealed" but it's still possible to push new grease into the bearings. I then reassemble and test. My test was to run the dynamotor for 15 minutes while monitoring its output voltage (+260vdc) and the running current. No problems were experienced so the dynamotor was ready to mount to the stripped chassis.

Finding Components - One thing I found out was that none of the R-648 manuals, that I had copies of, provide a parts list. Only one photo of one side of the dynamotor chassis is in the manuals. The schematic for the module is called "simplified" but it's the complete schematic. Luckily, the sheet metal had silk-screened component locations that helped in getting the correct locations for remounting the new (replacements for the missing originals) components. Fortunately, the 1.0H choke was not removed but the other three chokes were missing. The original 4K regulator load resistor, about a 5 watt resistor, had been replaced with a 1/2 watt carbon resistor that had become severely burned. Once I had found all of the replacement parts I was ready to rebuild the dynamotor chassis. 

Building the Dynamotor Circuit - Without a good photo of an original R-648 dynamotor chassis, I was pretty much left with fitting everything into the small front area. I used ground lugs and tie points as necessary. I followed the silk-screened positioning if it was possible (most of the time, it was.) Of course, the components aren't anything like the originals in appearance but they are the correct values. The +250vdc chokes were easy but the +27vdc chokes had to carry 2 amps so the wire for those chokes had to be at least 18ga or so. Once the circuit was built, I had to test the operation and voltages. With +27vdc input on pin 10 (+) and pin 11 (chassis and -) I had +260vdc, +150vdc and +33vdc on the proper pins of the connector. This completed the test and the dynamotor chassis was then installed into the R-648. Building the Power Cable - I gave KDWC some measurements and pin orientations and he was able to find the correct seven pin power connector identification number. From this, he located a used connector on eBay. Upon receiving the connector, I removed the wires from the pins. Only four pins are used for the R-648. Audio output is on pin A, +27vdc is on pin E, Chassis Ground is on two pins, B and D. The wires need to be 16 gauge on the power pins and 22 gauge is large enough for the Audio Output. The proper size wires were taped together and then a braided shield (harvested from old RG-8 coax) was installed and the entire cable wrapped with electrician's tape. I made the cable six feet long. The connector was installed on one end with the shield connected to a chassis-ground pin. On the other end of the cable spade lugs were soldered to the wire to allow a good connection to a +27vdc power supply. I used an old linear supply good for 10 amps - overkill, no doubt, but solidly stable.
Routine Problems - Before going any further, I needed to test all of the tubes. I was surprised to find that three of the 5749 tubes in the IF module were bad and both 5726 tubes were bad. All other tubes in the receiver tested good. Odd that most of the tubes in one module were defective. Anyway, a quick test of the receiver with ALL good tubes installed and the performance improvement was very good but there was a problem that involved all of the bands below 4mc.

Weird Problem - I had run the R-648 a little when it operated on 120vac so I thought that it was performing correctly. Now, with the dynamotor installation complete and good tubes in the set, I tested performance more thoroughly. Reception from 4.0mc on up to 25mc seemed normal with plenty of sensitivity and dial accuracy. Below 4.0mc, the sensitivity dropped dramatically to where no 75M ham signals could be heard. On 2.0 to 3.0mc no signals were received. Oddly, on 190kc to 500kc an AM BC station was tuned in at around 350kc. With the receiver on the bench, a signal generator was used as a signal source to confirm that below 4.0mc, the R-648 was not operating correctly.   >>>

>>>   Further testing revealed that 2-3mc and 3-4mc bands seemed to be "tuning backwards." This had to be some type of mechanical problem. I checked over the description and the drawing of the gear box. The description said that below 4mc, the receiver tuned counter-clockwise to increase frequency. Hmmm. Mechanically, the tuning was the same on all bands - clockwise to increase. Finally I read the description in the section before the low frequency mechanical tuning. I read that the gearbox always tunes the same direction and that the "appearance" of tuning counter-clockwise was due to a sliding mask over the dual, opposing dial scaling. The mask switching was cam-driven and changed scales at 4mc. In my case, the dial mask wasn't moving at all. The problem was caused when I had replaced the front panel with an original condition panel from Fair Radio. I hadn't noticed that inside the dial cover the spacing between the dial mask and the left side dial lamp was really, really small. I had the dial cover too close and too low and that was blocking the dial mask from moving. I installed a second dial cover spacer taken from the old "hacked up" front panel to give a slight bit more clearance. Upon reassembly, the dial mask now operated correctly and the tuning followed exactly what the manual instructed it should.
Test and Alignment - I noticed that the slug rack for the 190kc to 550kc was way out of mechanical synchronization. This particular slug rack is very easy to realign only requiring pushing the spring-loaded gear rack back and sliding the slug rack into the correct position. All other mechanical synchronizations were correct. The IF alignment requires accessing the switch arm S402D to input the 500kc signal, otherwise it's straight forward. There's also a PTO output transformer that needs to be matched to the IF frequency. The Variable IF consists of two bands, 2-3mc and 3-4mc and the alignment is by slugs for the low-end and trimmers for the high end. The various 1mc wide bands are set-up by the various crystals in the Crystal Oscillator that are operating at either the fundamental, 2nd and 3rd harmonics and then mixing with the PTO and the Variable IF. The exception is the 2-3mc band and the 3-4mc band which both are single conversion and bypass the Crystal Oscillator. Alignment of 190kc to 550kc and the bands from 4mc to 25mc are via slugs and trimmers in four sets of RF transformers. Once all of the mechanical issues were resolved the actual alignment was easy,...well,...sort of. Alignment Using Nav Manual - To say that the Nav manual is difficult to use is an understatement. First, errors abound. The alignment procedure has so many misidentified components that a significant amount of time is spent looking for the non-existent parts and then trying to figure out what the actual part ID is. Even when the procedure is correct, the user is jumping from the alignment page to tables in other sections of the manual. The most serious error is the synchronization of S402 as the instructions list the wrong switch tab for mechanical alignment. The test points locations are shown in another section of the manual rather than with the alignment section. I read thru the alignment instructions first (a couple of times) and then added (in pencil) the actual locations of the specified test points before doing the alignment so I wouldn't have to keep jumping back and forth between sections. Penciled corrections were also added "as found." Certainly, after one has gone thru their first alignment of a R-648 and all of the test points and errors are then known, any subsequent alignments, of course, would be much easier. Be prepared doing your first R-648 and read the instructions first, make notes and that should ease the frustration somewhat. Probably the Navy figured that only their experienced techs that had been sent "to school" on the R-648 were going to be working on the receivers so the convoluted and inaccurate instructions wouldn't be too serious of a problem.
Performance - The R-648 does have a lot of gain and is a very sensitive receiver. The automatic switching for the GAIN control in CW or VOICE is actually very practical and makes the switch from CW (or SSB) to VOICE (AM) easily accomplished. Since in CW the GAIN controls the RF gain, SSB is easy to demodulate. Selectivity with the mechanical filters is excellent. The IF bandwidth has such steep sides that strong AM signals suddenly are heard and suddenly aren't heard as the receiver is tuned through the entire 9.4kc bandwidth (late-build receivers have a 6kc Voice MF.) The action of the AVC time-constant does sometimes block AM signals if they are tuned through their passband rapidly. Slow tuning in AM allows the AVC time to control the receiver sensitivity. Even though the CW bandwidth is only 1.4kc SSB signals sound just fine. Audio quality is pretty much communications-grade and it's easy to drive a 600Z ohm speaker to loud volumes. There's no "break-in" provided. If used as a station receiver you'll have to provide good isolation during transmit and reduce the GAIN as necessary (this would be for voice only, in CW the receiver can be used to provide a sidetone.) It's small size and light-weight makes the R-648 easy to locate within the station landscape. I'm using my R-648 set up with my DY-12 operated ART-13. The receiver operates on a +26.5vdc 6A power supply and transmitter dynamotor operates from a PP-1104-C DC power supply (+28vdc at 50+amps.) Pseudo Shock Mount - The mount that can be seen in the top photograph came with the receiver. However, it didn't really look this way when I got it. It had rubber feet and wasn't painted. I replaced the rubber feet with the proper type, metal and cushion type shock feet. I painted the shock mount black to sort of match the receiver. On the whole, while certainly not as "cool" as an original would be, it is better than having the receiver cabinet set directly on the table. Or worst, having rubber feet installed on the bottom of cabinet. Original R-648 shock mounts are rare but maybe one will turn up someday. Until then, this one provides the necessities well enough.   NOTE: An original R-648 shock mount did show up on eBay a couple of years later. The seller also had the receiver but that was on a separate auction. Needless to say, the shock mount sold for double the price of the receiver. The shock mount went for $300 and the receiver went for $150.

1967 Electronic Assistance Corporation R-390A SN: 974 - Restoration Log (2016)

The following write-ups are little different from my usual restoration write-ups. I've written this one in the form of a journal or log that has daily input as the project progresses. I hope this approach gives the reader an idea of the order in which the restoration-rework takes place and the problems encountered along the way as the work progresses. It will also show the reader about how long it takes to complete an R-390A that isn't in terrible condition but certainly was non-operational and incomplete.  - H. Rogers, Aug 2016.

July 16, 2016 - Ham & Hi-Fi, a vintage audio, vacuum tube and ham radio business in Sparks, Nevada, had its semi-annual Open House Sale today. Lots of bargains and "freebies." I was interested in a decent-looking R-390A that was priced at $70. Not complete by any stretch but I was pretty sure I had all of the missing parts. I asked owner Ethan, "Is this R-390A seventy dollars?," just to verify. "Yep!" Hmmm. I paid Ethan and went looking for a hand truck to move the receiver out to the car. When I returned, my old friend Mike W7MS, was giving the R-390A a real "going over." "Well, I see the 3TF7 is still there. That's a surprise. It's missing a slug rack and RF coil though. I bet it's missing all of the crystals, too." Mike had flipped the R-390A over when I broke-in, "I already bought it, Mike." To which we both had a good laugh at the fact that Mike was critiquing my receiver purchase before I could even get it off the table.

July 17, 2016 - Once I got the R-390 home I was able to inspect it more thoroughly. Mike was right,...all of the crystals had been taken out of their sockets. There should have been 17 crystals and all were missing. The cover had been screwed down so tightly, I thought that nobody had been in there,...ever. Also missing was the 4-8mc RF-Ant transformer, the 4-8mc slug rack and slugs, all of the tubes in the RF deck, top and bottom covers, the Utah plate, the front panel bushing for the KC tuning. Both meters were non-original types that were similar types but not correct. On the good side,...the dial had a security flip-down dial display cover, the 3TF7 was good, both 26Z5 tubes were present (and tested good,) the receiver was a 1967 EAC contact with the correct data plate and all of the modules were correct EAC with the correct contract number on each module. None of the sheet metal was "bashed" and, mechanically, everything looked okay. Luckily, I had a couple of "parts sets" and extra modules so the missing parts weren't going to be too much of a problem. The receiver was extremely dirty with loads of greasy, oily contamination that had very fine black powder mixed in. The receiver had obviously been stored in a garage or machine shop or some other location where oil and fine black powder would be everywhere.

July 20, 2016 - Started complete tear-down. All modules out, front panel off, all parts plastic bagged and tagged.

photo above: The 1967 Electronic Assistance Corp. R-390A Order No. FR-36-039-N-6-00189(E) - SN:974 after the rebuild. Though these late-version receivers look exactly the same on the exterior, inside are where several changes were incorporated as the receiver design evolved. Most changes involve the types of capacitors used with these late-versions which use many ceramic disk and metal film capacitors instead of the paper dielectric types used in the earlier receivers. The PTO will be built by Cosmos Industries. A different crystal oven-crystal cover is used on these later receivers. The security dial cover is found on some receivers and is shown in the "raised" position.
July 21-23, 2016 - Cleaned front panel. I was amazed. I thought the front panel was kind of rough but it was all just the oily dirt and black powder getting into the engraved nomenclature. Careful cleaning first with WD-40 and a soft brush followed by Glass Plus to remove the WD-40 residue resulted in the front panel looking first-rate.

Complete disassembly of the Main Frame was necessary because the oily dirt had worked into the side panel joints due to loose screws. Again, under the dirt everything was in excellent condition.

July 24 - 28, 2016 - Took RF deck outside for a WD-40 flush of the gear box. The Veeder-Root counter was very dirty and I thought the digits were damaged but, again, it was just the black dirt causing the problem. Luckily, it comes off easy with WD-40. Stripped down the RF deck by removing all 24 RF and VIF transformers, slug racks, return springs. With no load, the KC tuning was checked for "feel" which was normal. Same for MC tuning. Checked cam synchronization by setting tuning to 07+000 and found that the 4-8mc cam was way off. Probably why the 4-8mc RF coil was missing - a former owner was chasing a problem in the wrong area of the receiver (also noted that the mica capacitors had been replaced in remaining two 4-8mc RF transformers.) Mechanically reset the 4-8mc cam to correct position. Replaced the missing 4-8mc transformer and also replaced the remaining two that had been "worked on." All other cams were in alignment. Cleaned and inspected ALL 24 RF & VIF transformers checking for proper rotation of trimmer on each. The replacement 4-8mc RF coil needed to have the trimmers "unstuck" and repaired before it could be used. Cleaned all slugs of dust and any other dirt. Cleaned all slug racks and lubed cam rollers. Reassembled the RF deck, adjusted the fit of all slugs into their respective coil barrels and then checked operation of all of the cams, slug racks, slugs and cam rollers.
July 29 - 31, 2016 - Installed a set of crystals in the RF module-Crystal Oscillator (17 crystals required.) Cleaned rotary switches. Reinstalled the RF module back into the Main Frame. Cleaned and lubed all controls and switches for front panel. Remounted harness and all controls to the front panel. Installed two #328 bulbs in the dial cover (originals gone.) Mounted front panel to the Main Frame temporarily - checking for fit. I only installed four screws since this panel will have to be "dropped down" for PTO end-point adjustment and probably for other things, it's best to just mount it in this manner for now. Original knobs were rough. Since I had a full set of restored knobs, these restored knobs were mounted to the control shafts.

August 1, 2016 - Tested the two can electrolytic capacitors and found the triple-30uf to have one defective section. The dual-45uf seemed to reform okay but the values are not very close. Same with the two good sections on the triple-30uf. I will have to rebuild these two units using new electrolytic capacitors for best reliability and performance. I had several spare R-390A can electrolytics and when testing them I found that ALL were defective in some way. Probably time to admit that you can't use and reuse the original, fifty-year-old caps anymore. New electrolytics ordered and on the way.

August 2 - 6, 2016 - While waiting for the replacement electrolytic capacitors, I tested all of the tubes and cleaned the tube sockets on the IF module and re-installed it into the Main Frame. I also had to locate tubes for the RF module since all were missing. The other modules all had W.P.M. heat-reducing tube shields so I also needed to find tube shields for the RF module tubes. All I had was IERC-type, which are very good heat-reducing tube shields, but they don't look like the W.P.M.-types. Since most of the tubes in the RF module are covered by the Utah plate, I went ahead and used the IERC-types.

August 7, 2016 - I can't find a 6DC6 (RF Amplifier) anywhere in the R390A spare parts or in any of the tube boxes. I will have to order a couple. They aren't expensive tubes but I never seem to have any NOS ones around for some reason.

August 8 - 11, 2016 - Rebuilt the two multi-section electrolytic capacitors. Photographed for the added write-up on this procedure that is now in this web-article in the Audio Module section. Picked up four NOS 6DC6 tubes from Ham & Hi Fi. Installed the remaining modules into the main frame.

Since I didn't set the Veeder-Root counter to XX.000 before removing the RF module, the PTO was not pre-set to 3.445mc. This is a minor inconvenience that requires the PTO be set by powering up the R-390A and measuring the frequency out of the PTO with a digital frequency counter. The procedure I use is above in the PTO section of this web-article.

Since I had already powered up the R-390A, I went ahead and hooked up a 600Z ohm speaker. I had lots of noise but the calibrator seemed pretty weak on 40M. I connected an antenna and tuned around 40M and heard a few SSB stations. Now this R-390A has been completely apart and is certainly quite a bit out of alignment but still it picked up a few signals. This should be a very good sign of things to come.

August 12-14, 2016 - I've been checking out performance of the R-390A before alignment by listening to various signals on different bands. This gives everything a chance to operate at voltage for awhile to make sure everything is going to function. Since the only "repair/changes" occurred in the 4-8mc RF section with the installation of different RF transformers along with different slugs and slug rack, it was kind of a surprise that the 4mc, 5mc, 6mc and 7mc bands actually would tune in the Calibration oscillator. I was really pleased with the performance on the bands 8mc and up. I had manipulated all of the trimmers on all of the RF and VIF transformers to verify that the trimmers weren't stuck, so I was surprised that 20M and 19M SW performed quite well. I checked for the Calibration oscillator signal on all bands and it was present. I tested the end-point error on the PTO and found it to be 8.0kc. That's the greatest EPE that I've ever encountered, so we'll have to see if the compensation adjustment can correct that much error. I dropped the front panel since that was going to be necessary for the EPE adjustment. I installed all of the correct hardware to mount the correct type meters and soldered the connecting wires up for both meters. After the EPE adjustment I will be able to fully mount the front panel with all screws and washers and proceed with the full IF, VIF and RF alignment. August 15-17, 2016 - See PTO section on Cosmos PTO. I added my experience with this Cosmos to that section of this article. The EPE adjustment is virtually inaccessible from the front through the locking plate and the front and rear gearbox panels. I had to remove the PTO each time to make the adjustment and then reinstall to test. Very time consuming. I was able to adjust the EPE from 8kc down to 0.5kc. Remounted the front panel with all screws, locking washers, shaft bushings, etc. Checked output on the Crystal Oscillator section and adjusted all trimmers for peak output.

August 18-20, 2016 - Peaked the mechanical filter inputs and outputs. This requires having the IF module dismounted but still connected to power. Photo and method described in "IF Module" section further above in this article. All mechanical filters were pretty close so, just minor tweaking.

August 21, 2016 -  Completed the full alignment. Most adjustments were pretty close but, as expected, the 4-8mc section was quite a bit out of alignment. Installed the Utah plate, top and bottom covers. Connected receiver to the full-size ham antenna. 40M reception is normal now. All other bands are functioning correctly. Adjusted Carrier Level Meter and IF Gain for best performance.

1967 EAC Performance and Observations - Here's what I've noticed on this receiver that is somewhat different than the earlier versions, such as the Collins or Motorola R-390As.

1. Components - many ceramic disk capacitors in RF and IF modules. These modules also have several capacitors that appear to be metalized film capacitors. The AF module appears to have similar capacitors to the old Vitamin-Q types but I think the construction is different with better seals. Certainly the multi-section filter capacitors are of the same construction and questionable reliability. They have the same problems that are found in any electrolytic capacitors that are half-a-century old. Overall, the capacitors seem to be better types than those used in the R-390As built in the 1950s. Cosmos PTO is difficult to adjust the EPE due to the new location of the L701 adjustment behind Z702.

2. Performance - is definitely equal to a rebuilt and recapped earlier version receiver. IF Gain is set at about 60% which is pretty close to where it's adjusted on the recapped earlier versions. With IF Gain set at 60%, most SSB signals demodulate nicely with the RF Gain at about 5 to 7 and the AF Gain at 7. This is using a 135 ft center-fed tuned inverted-vee antenna. SW BC stations usually run about 50 to 60db on the Carrier Level meter depending on the station and the time of day. The coupling capacitors in the AF module were NOT changed to .02uf but the audio sounds very good with noticeable bass response on AM BC and SW BC. Also, strong SSB stations and AM ham signals seem to have good bass response with the original .01uf coupling caps. Overall, a nice performing R-390A that is going to be set up with one of my ART-13A transmitters for awhile.

Time to Complete Project - It took just about one month to complete the rework on the 1967 EAC. This is from a non-operational, incomplete receiver to an entirely functional and totally complete receiver. I didn't work on the receiver everyday so total time actually spent on the project was probably around 20 hours.

Update - Sept. 4, 2016 - I guess I should have cleaned the Antenna Input relay contacts. The procedure is described in the Main Frame section further up this page. It's not difficult to do, even if the receiver is already back together. The symptoms were no (or very little) carrier level indication, a change in the normal position of the ANT TRIM for resonance and relatively weak signals. If STAND BY or BREAK IN were actuated then the signals would return to normal levels. This was the typical indication that the antenna relay contacts were introducing some resistance due to poor contact. In this particular case I don't believe the cause was oxidation because inside the arm, NC and NO were very clean looking. I used just a slight bit of DeOxit and paper to clean the contacts to have them measure zero ohms. Problem might have been some kind of rosin-like coating or something that dissolved with DeOxit. Other than this minor and easy to correct problem, the '67 EAC R-390A has been performing very well.

Update - March 7, 2018 - Read "Creating an Authentic Arvin R-725/URR" in Part 3 to see what's happened to this '67 EAC R-390A. Here's a quick link R-390A Part 3


Not Another 1967 EAC Restoration Log?

May 24, 2017 - I saw this R-390A at yet another "Open House" at Ham and Hi Fi in Sparks, Nevada last year. It was $100 "as-is." The yellow power cord and the 600Z matching transformer mounted on the back panel must have scared off any potential buyers, including me. I was tempted though, since the receiver had both original meters. I "stewed about" this R-390A for awhile and would usually go into the back storage area at Ham and Hi Fi just to see if it was still there. Finally, about six months had gone by and I was again looking at the R-390A that had a 1963 Imperial Electronics tag on the front panel. I asked Ethan if it was still for sale since it had been stuck way in the very back of the building for months. "Sure, I was asking $100 for it at the last open house. Is that okay?" I replied, "Yeah, the parts on the front panel are worth that to me." So, into the truck went this newest R-390A.

When I got the R-390A home, I had to investigate that yellow power cable and 600Z ohm transformer. The yellow cable certainly wasn't original but its installation didn't do any damage either. Same with the 600Z transformer that was utilizing an existing stud for mounting. While looking at the back panel I noticed "Electronic Assistance Corporation" with the "FR-36-039-N-6-00189(E)" order number and the "DAAB05-67-C0115" contract number stamped on the back. I then looked at the Crystal Oscillator (attached to the RF deck) and saw the same stamping. I noted that the electrolytics on the Audio Module were date-coded "67." So, I pulled out all of the modules except the RF deck and to my surprise they were all 1967 EAC modules on the FR-36-039-N-6-00189(E) order and DAAB05-67-C0115 contract from 1967. This receiver was a 1967 EAC R-390A that for some reason had an Imperial Electronics tag installed. Further inspection revealed that the receiver was nearly complete and original. The only missing parts were the correct ID tag and the "Utah plate."

Although I had originally thought when purchasing this R-390A to use it as a parts source for my 1961 Capehart (with OD front panel) this one is just too nice and original for that purpose (the Capehart will just have to wait.) I'll get started on this '67 EAC during the summer and write a restoration log as I proceed along with the rebuild.

June 12, 2017 - Started on this EAC. I had already obtained an original Utah plate and a repro '67 EAC data tag. All the modules except the RF module had been pulled and were setting with the receiver. I started with the IF module, the AF module and the Power Supply. Each module was cleaned and the tubes tested. Any weak tubes found were replaced. The two electrolytic filter capacitors were reformed. These capacitors were date coded 1967 and both checked okay. Reforming seemed normal with the two 40uf caps drawing about 10uA after reforming at 280vdc and the three 30uf caps drawing about 15uA to 25uA at 280vdc after reforming. The final test will be to see how the filter caps perform in the receiver. I didn't have very good luck with the last EAC receiver's filter caps which had to be rebuilt. These filter caps seemed to form nicely but performance is the final test.

June 13, 2017 - Completed cleaning and tube testing on the above modules. I had to double-check the wiring on this EAC power supply as the wiring didn't look like most PS modules. Though the wires were not "tucked" under the chassis, as is normally done, the wiring was correct. Just an anomaly of that particular PS assembler and final inspector. I had to replace all of the 5749 tubes in the IF module since they all tested weak. They were all RCA-JAN brand and date coded 1965. Also, one 5814A in the IF deck needed to be replaced. On the AF module I replaced one 5814A. Both 26Z5 tubes checked okay in the PS module.

June 14, 2017 - Tested the tubes in the RF module. All were weak except two 6C4 tubes and one 5814A tube. Checked cam synchronization at 7.000+ and found all cams to be close. Looking at the photo of the receiver to the right one can see the UEW Union sticker applied to the front panel below the Carrier Level meter. I tried Glass Plus and Goof Off with no effect. WD-40 however was able to loosen the glue and the sticker came off without leaving any residue. Why someone would apply any kind of sticker to a high-level communication receiver panel is unknown and seems like something that an 11 year old would do. Luckily, it came off with no issues. Cleaned the front panel with Glass Plus. This was just a quick cleaning to see what the overall condition was and it was excellent. The knobs were also in excellent condition. The Main Frame sheet metal was also in excellent condition with no corrosion. I put the Main Frame with RF deck and PTO installed on the bench for further "tear-down." Photo to the right shows the receiver before tear-down. Note the UEW sticker adjacent to the Function switch.

June 19, 2017 - Pulled PTO, no backlash spring on coupler. Pulled RF deck. Cleaned Main Frame bay. Disassembled RF deck for WD-40 gear wash. Roller came off of slug rack on the 18mc-32mc rack. Retaining washer missing. Will have to assemble another 18mc-32mc rack with the slugs from this receiver.

June 21. 2017 - Did the WD-40 flush on the gear box. There was some kind of grease coating on the cam surfaces that had dried hard. Had to scrub with acid brush and WD-40 to remove. No other problems. Gear box has very light "feel" now. Was pretty "stiff" to begin with. After cleaning up the WD-40 residue, removed all RF and variable IF transformers for inspection and cleaning of bed plate and contact pins-sockets.

June 22 - 25, 2017 - Cleaned and inspected all 24 RF-Variable IF transformers. Checked trimmers for proper operation. Cleaned pins with DeOxit. Re-installed all transformers. 18mc-32mc slug rack roller bearing was defective. Replaced slug rack but installed the original slugs (they were the late-versions with "Collins" on them.) Cleaned and lubed slug racks and bearings. Adjusted all slug mounts for best alignment with the slug barrel of each RF-Variable IF transformer. Checked mechanical operation. Aligned two slug rack lifter cams for better alignment at 7.+000. Holder for dual crystal assembly was missing. Installed holder robbed from "parts chassis." Checked switch alignment for Crystal Oscillator. RF module is ready to re-install into Main Frame (except for tubes.)
June 26 - July 1, 2017 - Installed new AC power cable with military metal AC plug in Main Frame. Cleaned inside and rear panel of Main Frame. Installed RF module into Main Frame. Cleaned the backside of the front panel. Remounted front panel and secured harness clamps. Cleaned all knobs. Installed IF module, PS module and AF module. Cleaned PTO. Checked the 5749 PTO tube - it was bad so installed NOS 5749 tube. Installed PTO into Main Frame. Since I had removed the PTO with the Veeder-Root counter at 07+000 (and I hadn't changed the position of the PTO shaft) I set the counter to 07+000 and then while installing the PTO I also installed the oldham coupler disk. The PTO was difficult to install so I loosened the rear PTO mount at the two screws that secure the mount to the Main Frame. After the PTO was in position, I then tightened the screws securing the rear mount. Connected all cables and power plugs to all modules. Powered up the R-390A and, with the Calibrator and BFO turned on, tuned in 07.500mc to receive a "marker" signal. I then rotated the MC dial through its entire range from 00.500 to 31.500mc and heard the "marker" signal on all bands. This indicates that basically the R-390A is working on all bands but the receiver still needs to be aligned (since it was totally disassembled during the inspection, cleaning and testing process.) Connected a 20' wire on the floor as an antenna and tuned in WWV on 15mc and on 10mc. Also, a couple of SW-BC stations around 12mc. Although the R-390A did receive these signals, it was obvious that a complete alignment would be necessary (and expected.)
July 2, 2017 - Test that the mechanical ten turn tuning had proper over-range - +38kc and -30kc, which is okay. Tested end-point error. Odd in that linearity seemed poor. 0 to 200 was about 4kc, 200 to 800 was about 1kc, 800 to 1000 was about 3kc. If measured from 0 to 1000 the EPE was about 7kc but between 200 and 800 the EPE was only 1kc. Tested the actual frequency output of the PTO to see if the mechanical xx.000 to xx+000 is 3.455mc to 2.455mc. This shows if the PTO is actually synchronized with the Veeder-Root counter. I did a mechanical relationship in that I didn't change the PTO shaft after removal and installed it in the same position at xx+000 but that doesn't check that it was correct to begin with. The only true test is to measure the PTO frequency at xx.000 and xx+000. The PTO is synchronized to the counter. The non-linearity also can be seen by measuring the output frequency.

July 3, 2017 - I decided to swap PTOs with my other '67 EAC. When I get time, I'll correct the EPE on that PTO (or test it.) Meanwhile, the PTO I've installed has about 500 hz EPE and is linear across the 1.0mc span.

UPDATE - Sept.24,2017 - Checked out the non-linear PTO. With xx.000 = 3.455mc at +xx.000 = 2.458mc or about 3kc of EPE. However, if the frequency is tracked every 10kc the excursion out of linearity is as much as 8kc off. It appears that the PTO may have been checked at the end points which was 3kc off and not checked for linearity. Maybe this is one of the "rejects" that were sold directly to civilians. At any rate, this PTO could be disassembled and perhaps the linearity adjusted for better performance. This is accomplished by adjusting three screws on the rear threaded mount of the ferrite core. This "pushes" the position of the sliding linearity arm that rides on an aluminum rail which hopefully compensates for non-linearity by slightly moving the core over a fairly long span. I'm not really sure anything would be gained by going into the PTO. The actual non-linearity of this PTO can be compensated for by adjusting the CAL to the closest frequency and the resulting accuracy is about 1kc over a couple hundred kilocycles. Only when trying to hold 1kc over the entire 1mc range does the linearity error become apparent.

July 7, 2017 - Synchronized the newly installed PTO with 3.455mc and 2.455mc end points. Calibrated the BFO with WWV. Checked the Crystal Oscillator outputs at E-210. All were low and needed to be readjusted for peak. Set up to do the IF module adjustments next session.

July 9, 2017 - Peaked mechanical filter trimmers and stagger-tuned the IF transformers with no problems. When trying to peak the Amplified AGC LC the AGC voltage was <-1 volt and didn't change regardless of the input signal level. I had already tested the tubes and had good ones installed, so that wasn't the problem. I installed a test extension socket so I could measure some voltages on the 5749 AGC amplifier tube. On pin 5 the should be plate voltage but the measured voltage was <+1vdc. The only component between the 5749 plate and the B+ was Z503, the AGC LC network that is installed inside an aluminum can shield similar to the IF transformers. To confirm that Z503 was open, I measured the DC R which, of course, was infinite. I checked the schematic to see if there was any component that, if shorted, would allow too much current to flow thru Z503 but only the 5749 AGC Amplifier and the 5814A AGC rectifier were in the circuit. Z503 had to be replaced.

Z503 is not an easy component to remove from the IF module. The complete procedure is in the IF Module Rebuild section further up this webpage.

Once the Z503 swap was completed I reinstalled the IF module back in the receiver. When it and all of the test gear was powered up, I now had AGC voltage and I was able to adjust it to peak using Z503.

The photo to the right shows the location of Z503 on the IF module. The AGC Amplifier tube is removed to show Z503 better. Note the Carrier Meter ADJ pot to the left for reference to the location of Z503.

July 10, 2017 - Aligned the Variable IF section and the Crystal Oscillator variable transformers. Nothing unusual.

July 11, 2017 - Completed alignment doing the RF tracking including the balanced input adjustment. Operated the R-390A with the regular ham antenna and performance seemed normal. Carrier Level meter seemed a little light. With no antenna input I adjusted the Carrier Meter pot for a needle-width over zero. With the antenna connected, WWV on 15mc indicated around 40db. Could be conditions. Levels during alignment seemed normal. More listening necessary for better comparison. I stamped the repro EAC tag with the SN of 2172 which seemed like a good number.

Conclusion - Sort of,... - So, this '67 EAC was much more complete than the one I did last year but still it took about one month to complete the work. I have to admit I was distracted several times by other projects. Still, I guess one can figure if the receiver is very complete and in pretty nice condition then a minimum of one month for a complete tear-down, check-out, tube testes, some repairs, reassembly and alignment.

Update - July 13, 2017 - I have this '67 EAC set-up as a station receiver and have noticed that the sensitivity is noticeably lower on the 2.0 and 3.0mc bands. Not so low it doesn't receive all signals but probably 10 to 20db lower than the 1.0mc band or any band 4.0mc and up. This usually indicates that the 2.0-4.0mc RF-Ant input transformer has taken some high level RF that "burned" the coil. I had inspected all of the 24 RF and Variable IF transformers earlier and everything appeared perfect. However, performance tells a different story. To verify, I'll swap the 2-4mc RF-Ant input transformer with a "known good one" and see if there's an improvement. More details after the test,...

I swapped the 2.0-4.0mc RF-Ant Input transformer from the '67 EAC SN: 974 since I knew that one was operating correctly. Using the 100kc Calibrator as a signal source, I measured about 20db at 3800kc with the original transformer installed. After the swap, the 100kc Calibrator signal was 45db at 3800kc, which indicated that the original transformer had a problem. Very, very close inspection of the original transformer revealed a small burn mark that indicated that there had been excessive RF input to the receiver while it was tuned to 80M. This seems to be a common problem that I've found on almost half of the R-390A receivers I've worked on.

Eventually, while I was converting this receiver into a "black panel" R-390A, I discovered the actual cause of this problem. I think the small burn mark was my imagination. Read "New for 2022" in Part 3 to see what has happened to this R-390A receiver,...there's a link to Part 3 just below,...




R-390A PART 1                     R-390A PART 4                     Return to Home Index



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