NATIONAL CO., INC. - HRO RECEIVER
Restoring E-50 - 2nd Production Run Receiver
A Step-by-Step Chronicle of the Restoration Process
Some of the Processes Covered Include:
Stripping and Painting the Chassis
by: Henry Rogers WA7YBS/WHRM
This article started out as an additional section in "National Co., Inc. - HRO Communications Receivers - "The Cream of the Crop" that was to document the restoration of a donated HRO receiver that had an interesting provenance and an early production history - likely the 150th HRO built. I decided then to actually write the sections as I performed the work, thus giving a chronological order in how the restoration process was being accomplished and a certain "freshness" to the descriptions. About halfway through the project I realized that this "addition" was going to become far too lengthy and would have to be edited down for "Cream of the Crop." However, the processes described were detailed and provided a reference to the several different restoration tasks performed - information that might be useful to other restorers. So, here it is as a full-length article with almost all of the photographs taken during the restoration project. H. Rogers - Jan. 2012
The History of E-50
E-50 was donated to the Western Historic Radio Museum by Jim Larsen AL7FS of Anchorage, Alaska in September 2011. E-50 was given to Jim by Val Anderson of Seward, Alaska. In the 1940s, E-50 was owned by Anderson's brother-in-law, Carl Carlson of Anchorage, Alaska. Carlson may have gotten E-50 through his son-in-law who worked for the CAA in Alaska at the time. By the 1950s, E-50 had gone to Cordova, Alaska and when Carlson died in the 1950s, the receiver was shipped to Val Anderson. It seemed that E-50 had spent most of its existence in Alaska. The receiver was stored for many years in Anderson's basement and, due to the cold, humid coastal environment of Seward, E-50 now had some rust issues. Additionally, several years of modifications had left E-50's originality somewhat compromised. A couple of the modifications suggest that the receiver was rack mounted (possibly when used by the CAA.) The restoration of E-50 illustrates that sometimes the rarity of a particular receiver, in this case the 150th HRO built with an interesting and detailed provenance, requires the restorer to go to greater lengths than normal to achieve the desired results.
Assessment - The photographs to the right and below show
E-50 in the condition that I received it. Despite the "rough" appearance
of this HRO, it has enough of its original parts to proceed with a
restoration that will bring the receiver back to original design, great
appearance and full functionability. The S-meter is vaguely similar to
the original since it has a metal case and is not illuminated but it has
a later amber National scale in a metal case mounted with a flange. The
small skirted knobs are present as are the toggle switches. The original
push button switch for the S-meter has been replaced but the mounting
hole has not been modified. Luckily, I have an original type push button
switch for the restoration. The PW-D is missing the inner wheel and is
the later, painted type. I plan on recreating the nickel plated PW-D
from a lacquer finished one. This will require developing a technique to
achieve the "flat finish" to the plating rather than a polished, bright
silver appearance of typical nickel plating. The pilot lamp is not
original. Note that the coil set installed is from an HRO-5 and is the F
frequency coverage. I will add this coil set to my HRO-W set up and
replace it with a very early (and correct for this receiver) C coil set
that has the white background graphs.
The top of the chassis shows that two original tube sockets have been replaced with more modern octal sockets. These will be replaced with original sockets from an "HRO parts set." The addition of a seven pin miniature tube socket to the left-front part of the chassis presents a problem. Our hole filling technique used on H-103 didn't result in the quality I desired, so a different method is going to be used on E-50. The rust issues are probably going to require complete disassembly followed by rust treatment and a repaint. Only a few components but several tie points are mounted with rivets. Rivets can be a problem to remount and have the result look original.
|Corrosion on the aluminum parts will be treated with sodium hydroxide which will remove the corrosion and leave the aluminum with a flat finish, like original. Under the chassis is not too bad, considering that this receiver has had many modifications installed. There are still several of the National lead-end ceramic resistors left along with some of the original paper-wax capacitors. I was surprised at how many original parts were left under the chassis. As with H-103, we will recreate "new" components with combination "new-vintage" parts as described in that section above.|
Required - Since E-50 has some rust issues it's going to
be necessary to remove almost all of the parts from the top of the
chassis. This will allow access to areas that were under IF cans or the
Crystal Filter assembly. Also, with all of the parts removed the entire
top of the chassis area is easy to work on and remove the rust.
With major components, like the tuning condenser assembly or the IF transformers, it's easy to perform an inspection and test at this time. This allows finding replacements, if necessary. Any restoration work required is much easier to perform when the piece is removed from the chassis. Our preliminary testing showed that the Crystal Filter assembly, the two IF transformers and the BFO assembly were all in good electronic condition. The aluminum shields needed cleaning but otherwise these parts were usable.
The tuning condenser and PW Gear Drive had some visible problems. First, the fiber insulators that carry the rotor contacts were somewhat warped. It appears that the fingers are still in contact with the rotor but certainly this illustrates why National replaced this material very early in production. Also, it was noted that a former owner had filed a "knob flat" onto the tuning shaft. This was certainly not necessary because any marring of the tuning shaft will result in extreme difficulty removing the PW-D dial when in the future that becomes necessary.
I keep all of the nuts and screws along with the smaller parts in a meter box. You can sort the parts and identify their use by keeping them in plastic bags with the parts location written on the plastic bag. I've assembled a lot of HRO receivers, so the box works for me. Searching through one of my HRO parts boxes turned up the replacements for the missing tube shields and caps. Also, I found a suitable PW-D micrometer dial that is complete although it will be necessary to modify this dial to become a Nickel Plated PW-D.
Shown in the photo to the right is E-50 with all of the major parts
removed from the chassis. It is still going to be necessary to remove
the tube sockets for cleaning and repainting.
|The Easy Stuff
First - IF
Transformers and the BFO Assembly - The condition of E-50
warranted a close look at the IF transformers. It was noted that the 2nd
IF transformer was mounted "inverted" from the normal National mounting
indicating that it had been removed from the chassis in the past. A
quick test indicated that the 2nd IF transformer had continuity but both
coils were loose on the wooden dowel that is used for mounting the
coils. I had to use bee's wax to remount the coils to the dowel. This is
important because the placement of the coils in relationship to each
other determines the coupling and therefore the gain and selectivity of
that particular IF transformer. The BFO coil circuitry is also contained
in a shielded can. The BFO coil was also loose on the mounting and had
to be remounted using bee's wax.
It was noted that since an octal tube had been installed for the Detector/AVC, there was no grid lead routed through the chassis eyelet as original. Apparently, the modification was to use a 6SQ7 single-ended tube which has the grid connection at the socket. I installed a new longer detector lead that exited out the bottom of the IF can in order to eventually use the correct 2B7 Detector tube in the receiver. Additionally, a correct grid lead will be added to route through the chassis eyelet and provide the grid connection to the 2B7 tube. I also had to install new grid leads on the 2nd IF transformer and the BFO coil. I duplicated the color of the original leads by using white cloth covered stranded wire and coating the cloth insulation with amber shellac that was wiped off quickly. This gave the leads a yellowish-tan look that was close to the original color of the grid leads. The grid lead installation is not complete in the photo to the right. Black shrink tubing has to be added over the solder connection to the grid cap clip. The IF and BFO cans have to be installed on the chassis and the tube sockets and tubes installed to determine the exact length needed for the grid leads, then the installation of the grid cap clips can be finished.
|PW Gear Drive
- The PW Gear Drive needed attention. When removing the gear box top
cap, it was noted that the gear box was devoid of any grease. This is
unusual since "dried yellow grease" is normally what is found. When the
worm gear-tuning shaft was removed by dismounting the elliptic bearing
hub, it was noted that the assembly was incorrect and that the ball
bearing was next to the worm gear flange. This has the worm gear-tuning
shaft only supported by the conical thrust bearing and the front of the
elliptic bearing hub. The anti-backlash springs were installed
correctly. I had to replace the original worm gear-tuning shaft since a
"knob flat" was filed onto the shaft that made the PW-D dial difficult
to remove. This shaft should be round and not marred so the PW-D can
easily be installed or removed. After a thorough cleaning with light oil
(I use WD-40,) the worm gear and the split-gears were lubricated using
light weight grease (I use a moly-grease designed for thrust and ball
bearings.) The anti-backlash gears were set at two teeth and the
replacement worm gear-tuning shaft installed (salvaged from an HRO parts
After some testing of the PW-Gear Drive actually mounted and driving the tuning condenser, the following was noted. The operation seemed to slightly "bind" randomly and the operation of tuning was noisy with a "springing" type noise being heard as the PW-D was rotated. I removed the PW-D to confirm that the problem was with the PW-Gear Drive. I reset the anti-back lash to confirm that it was set at "two teeth." During the rebuild I had replaced the original elliptic bearing hub with one from the parts set. I had noted that the "parts set" elliptic bearing hub had been slightly damaged by some former owner filing around the hub. This is sometimes found when an inexperienced technician has trouble refitting the PW-D micrometer dial. The uneven filing was causing the random binding so I refitted the original hub. Even though the original hub had some wear, it was "even" wear and therefore didn't cause the rough feel and random binding. After this re-adjustment and the replacement of the original hub, the PW-Gear Drive and the PW-D tuned the condenser with ease and smooth, noiseless operation.
- The next step was to thoroughly clean the tuning condenser. Most of
the grease was removed using denatured alcohol and a long handle paint
brush. Particular attention was paid to the rotor contacts since these
are mounted to the rough-cut fiber insulators that divide each of the
four sections of the tuning condenser. Since the fiber appeared to be
warped, I was concerned as to whether or not the contact to each rotor
hub was sufficient. These contact areas were cleaned with De-Oxit and
the bearings were lubricated with 10W sewing machine oil. After a good
cleaning, I tested the tuning condenser with a capacitance meter and was
surprised at the accuracy of the entire unit. I set the first section to
100pf and noted that the other sections were within 3pf of each other -
The mounting base's paint was in rough condition from years of grease and oil along with some major scratching due to a modification grounding lug mounting. The base was removed and given a new black nitrocellulose lacquer paint job. The top cap of the PW-Gear Drive was also repainted. This cap always seems to get a lot of wear due to its location right at the top of the assembly. After the black lacquer was dry, the red fill was applied.
Next - Restoring the Chassis - The photo to the right
shows the non-original octal socket that is installed for the Mixer
tube. This is directly behind the tuning condenser mount. Though the
rust looks severe, I haven't attempted any cleaning or removal at this
point. This condition is still "as received." Hopefully, when the rust
is removed and the surface prepared, it will be difficult to tell that
there was any damage. Also, note that the grid cap in the foreground is
for an octal tube. This will have to be replaced with the correct
National grid cap along with the replacement of the octal socket with
the correct National ceramic six pin socket and shield collar.
Additionally, another ceramic socket, a large seven pin type, will be
required for the Detector since that tube socket was replaced with an
octal type socket.
The first step in restoring the chassis is to remove all of the circuitry and all of the rivets and screws that comprise the mountings employed. The rivets are first drilled to weaken them and then they are "driven out" with a small hand punch and hammer. There are two eyelets that shouldn't be removed, one under the Crystal Filter assembly and one for the Detector tube grid input. These eyelets are for a wire to pass through the chassis from underneath to the topside. There are three coil guide/ground pins that are staked in so these should be left in place since reinstallation would require special tools. The eyelets and the coil guide/ground pins will be masked when the chassis is re-painted.
Note in the photo below that when the mountings are removed the entire "circuit" can be extracted from the chassis intact. This will ease the reassembly since we won't have to do too much "rewiring."
|When the chassis was "stripped" of all parts and assemblies, the rust removal could begin. I decided to avoid the chemical approach of rust removal since the results still require sanding to bare metal. I just removed the rust by sanding with progressively lighter paper until the chassis rust areas were either bare metal or, though discolored slightly, a very smooth finish. Notice in the photo to the right that some areas still have paint. Since I am re-spraying with nitrocellulose lacquer (as original) there will be no problem spraying over the original paint as long as the edges are smooth and "feathered."||
- This is a common problem encountered with almost all HRO
restorations (and many other vintage receivers, too.) The photo to the
right is a close-up of the modification hole that was used to mount a
miniature seven-pin tube socket. Interestingly, the tube socket was
never wired to anything, just mounted. Though there were four other
modification holes on the chassis, these were small screw holes that
didn't present any problem to fill. I used aluminum duct tape as a
backing on this large hole since the Bondo used as filler doesn't have
the viscosity to stay in place with this large of an opening. The tape
provides a backing that the Bondo won't stick to and when the Bondo has
cured, the tape can be removed and the back side might be usable
"as-is." Usually not though and you'll probably have to do another Bondo
application on the backside to smooth where the tape was. The smaller
screw holes don't need the backing and the Bondo can just protrude
through the hole since it will be sanded flat later.
Modern Bondo cures rapidly. Usually in about five minutes it is beginning to harden and by ten minutes it should be "rock hard." The good news is that Bondo is very, very easy to sand into either a shape or a flat surface. You can rough remove the excess after about 20 minutes but the fine sanding shouldn't be done for about an hour. Fine paper will allow blending the surface of the Bondo fill to the surface of the chassis. When painted, the fill won't be noticeable.
Note in the photo below-left, the serial number, E-50, is quite visible since the paint is removed.
|Chassis Painting - Fortunately, many years ago I bought a gallon of Gloss Black nitrocellulose lacquer. This is what most black paint used in the thirties was. Today, it is almost impossible to find this kind of lacquer since the industry has gone mostly to acrylic lacquers and enamels. Since this was a small job, I used a small half-pint spray canister of the type available at many hardware stores (Pre-Val is the name.) This allows mixing your own paint and then having the ability to spray-apply it to your project. First, the chassis was cleaned with lacquer thinner to remove any grease or anything oily that might have been left from the rust removal. I also masked the two eyelets and the three coil guide/ground pins. The black lacquer was applied in three coats without any primer. This was how the chassis was originally finished, that is, without primer. As long as the surface is clean and smooth, primer isn't needed. Shown to the right is the finished paint job. The next step will be remounting of the major components.|
Reassembly - The plug-in coil finger contacts were
installed first. These must be mounted with the screw heads inside the
coil bay to allow clearance for the plug-in coil sets. After the fingers
were mounted a plug-in coil set was installed to see that the fit and
alignment was correct. I also temporarily mounted the tuning condenser
and PW-Gear Drive to see that everything was aligned mechanically. The
tuning condenser mounting base central bracket must mount between the
coil finger assemblies for the 2RF and Mixer contacts. Sometimes
mounting adjustment is necessary to allow for enough clearance for this
The tube socket collars require that an external tooth lock washer be placed between the bottom of the collar and the chassis. This is to assure that the collar has good contact to the chassis and therefore the tube shield, when installed, will be grounded. Eight of the nine tube sockets mount with screws, lock washers and nuts. Only the 2A5 AF Output tube socket is mounted with rivets. The 2A5 is the only tube without a full shield and therefore that socket doesn't have a collar. A partial shield is made from a right-angle piece of aluminum and this mounts by the 2A5 socket using screws, external tooth lock washers and nuts. Since the circuitry was removed intact, when installing the tube sockets back into the chassis the circuitry was also installed back into the chassis.
Cleaning the Tube Shields - The tube shields are made out of aluminum and therefore can easily be cleaned with spray-on oven cleaner which is sodium hydroxide. Only leave the oven cleaner on the aluminum for a minute or two or it will react with the aluminum and turn it black. I use a soft medium size paint brush (about a half-inch wide size) to gently work the oven cleaner and then rinse in water. The aluminum will look very clean and flat but bright - almost like new. Don't rub the aluminum or it will polish and look incorrect. It should "air dry" to maintain its "flat" appearance. The aluminum tube collars and the angled tube shield for the 2A5 were given the same treatment.
|Crystal Filter Assembly
- Like many HROs, E-50's Crystal Filter, while electronically in good
condition, had a corrosion problem on the top of the unit. To correct
the problem would require complete disassembly since the corrosion would
have to be removed by sanding. Disassembly is easy since screws are used
for mounting. Two wires have to be unsoldered from the crystal socket to
remove all components from the main body. The crystal socket is riveted,
so it is left in place. With all of the components removed, sanding of
the top of the body can be accomplished. When all of the corrosion is
removed, the body was wiped down with denatured alcohol.
Early HRO Crystal Filter boxes are finished in a yellowish-gold coating. To give the raw aluminum the proper color, I coated the body where I had sanded using yellow-tinted clear lacquer. This gave the body the proper appearance. The original was a chemical coating called Irridite but since I didn't have that process available, the tinted lacquer gave a good approximation of the appearance. When the Crystal Filter was reassembled and mounted to the chassis it looked very close to original. A new grid lead was installed to match the new IF-BFO transformer grid leads.
New Audio and Antenna Shielded Cables - The two shielded cables that are under the chassis were replacements. Each shielded cable had a pair of plastic insulated wires inside - one green and one yellow - definitely not original. The original Audio Gain cable had three wires, each cloth insulated and colored red, yellow and black, inside a braided, tinned shield. The Antenna cable had two cloth insulated wires inside a shield, both colored black.
I built up these two shielded cables by using a length of RG-58U "test cable" which uses a tinned braid so I would have the correct appearance. By removing the RG-58U jacket the braided shield can easily be removed by just pushing the shield ends together to loosen the braid and increase the inside diameter. I found cloth insulated wires that were the correct color and then these were "pulled" through the shield. Then the shield was "pulled" tight by sliding the cable through my hands. To give the wires an aged look, the ends were dipped in amber shellac.
To install the shielded cables requires that the Antenna cable be routed over the Audio cable at a right angle. The Antenna cable runs almost directly from the Antenna terminals to the 1RF port to access the coil finger contacts. The Antenna cable shield is soldered to the Audio cable shield where the two cables cross. Also, there is a ground lug about one inch away that has a length of TC soldered to the Audio cable shield. At the 1RF Amp tube socket another lug is used to further secure the Audio cable by soldering to the shield.
photo far left: E-50 chassis partially assembled showing how the aluminum parts look after cleaning with oven-cleaner. All of the "fake rivets" are installed mounting the various parts that were originally riveted to the chassis. New grid leads are installed. The correct XC-6 and XC-7S ceramic sockets were donated for this project by well-known National Co. expert, Bill Fizette. They were installed when this photograph was shot.photo above left : Crystal Filter assembly after corrosion removal. The large self-tapping screws are original for early filters. Also, note that there are no bearing shaft supports for the Phasing and Selectivity controls on the early Crystal Filters.
photo above right: Close-up of 1RF finger contacts for coil set. Note the correct installation of the mounting screws with the nuts and lock washers on the top side. This allows the required clearance inside the coil bay for the installation of the coil sets.
|Making "Fake" Rivets - I did a great deal of searching and couldn't find any source for the hollow shaft, nickel-plated brass rivets that were originally used in the assembly. Even McMaster-Carr didn't stock anything like the original rivets. This is almost always the case when doing restorations where rivets were used in the assembly. What I do is make "fake" rivets using screws that I have reshaped the head to look like a rivet and then mount the part as if using a "screw and nut." I first obtained several stainless steel, slotted fillister head screws that are 6-32 and .25" long. I use stainless because it looks the closest to nickel plating and I use fillister heads because there is more material under the slot than in other types of screw heads. Each screw is chucked up in a drill press or a handheld driver (like a Makita) and then the screw head "slot" is removed and the remaining material is shaped into a "rivet head" using a file while rotating the screw head using the drill press or handheld driver. Final polishing is done with 400 grit aluminum-oxide paper and 0000 steel wool. >>>||>>> There are about 25 rivets used in the HRO, so the process is
laborious but the end result is each part can be easily mounted using a
nut driver to tighten the nut (since you don't have a screw head now.)
External tooth lock washers are mandatory because most of the
rivet-mounted parts were achieving chassis-ground via the mounting.
The four photos below show the progress of making a "fake rivet." The first photo shows the fillister head screw in the chuck ready to be filed flat. The second photo shows the screw head after being filed flat. The third photo shows the "fake rivet head" after shaping and polishing - it is now ready to remove from the chuck. The fourth photo shows some "fake rivets" installed around the 2A5 audio output tube socket.
HRO Cabinet and Panel Painting
Painting Moved Ahead
- The cabinet and panel are going to need to be repainted
using VHT brand Hi-Temp Black Wrinkle Finish (BWF) paint. This operation
has to be performed outside which puts us at odds with the Fall weather.
The plan is to complete the component remounting and essentially have
the chassis portion complete except for wiring corrections, component
rebuilding and actually getting the chassis operational. After this,
then we are going to devote time to completing the repaint of the
cabinet and panel which has to be finished by the first week in
November. After the painting is finished, we can return to the chassis
work while allowing the cabinet and panel paint to "cure." Actually,
when wrinkle finish is "dry to the touch" it is still very soft and will
easily mar with mounting screws and rough handling. This cure period
will allow the wrinkle to develop its full hardness before reassembly is
Paint Test First - Since I've never used the VHT BWF paint, I decided to do a test to see just how this brand reacts and how it looks. The instructions on the can are different than any other BWF I've used before, thus the caution I'm taking. For many years I used Illinois Bronze WF paints but they went out of business many years ago. Since then, I've been using Krylon's BWF since it was easily available locally at Kragen Auto. Kragen was recently purchased by O'Reilly Auto and this new store chain stocks the VHT brand and has dropped Krylon's BWF. The Krylon was very predictable and easy to use but the color was "charcoal black" rather than a deep jet black. The VHT test will also be for color along with wrinkle pattern.
|Paint Test Results
- VHT Hi-Temp BWF behaves just like any other one-part wrinkle finish
paint. I applied a "heavy coat" made up of five applications without too
much of a pause between the individual coats. The test piece was then
placed under a 100 watt incandescent lamp with an aluminum bell
reflector. Although the can instructions indicated an hour for the
"wrinkle" pattern to appear, the paint had entirely finished wrinkling
within ten minutes. Like other BWF, VHT is very soft until it has
"set-up" which takes a few hours minimum, although overnight is better.
The VHT "color" is very dark black and it's an excellent match for the wrinkles used in the thirties and during WWII for color. The pattern is very close to that used on the Hammarlund SP-100s and on the National RAO receivers. The VHT pattern is much better than the Krylon BWF pattern when it comes to matching the pre-war and WWII wrinkle patterns. There are some differences in many early wrinkle patterns and VHT doesn't have the minute fractures between the wrinkle peaks that is found on many of the thirties BWF. However, the VHT pattern has the "ripple" convolutions that are commonly found on a lot of early wrinkle finishes from the thirties up through the forties. This isn't exactly a commercial for VHT BWF but this paint is very black and has an acceptable wrinkle pattern.
Next will be stripping E-50's cabinet and panel for repairing the many non-original holes. Also, the lid "finger lift" was modified to be flat so the receiver could be rack mounted. This will have to be brought back to its original shape. Additionally, the front panel has "notches" cut in the side "wrap-arounds" that will need to be repaired.
Old Paint - The only stripper that works on the older
paints is Methyl-Chloride. This is dangerous stuff and the operation
must be done outside with good ventilation. You should protect you hands
by using Platex gloves - not the ones you buy in the store but
commercial-grade gloves that are made out of platex. These are the only
type that seem to be impervious to the Methyl-Chloride. I also put on
Nitrile gloves first then the platex gloves. Methyl-Chloride strips
paint because it has very small molecules that can enter the paint
structure and weaken it thus allowing easy removal. These very small
molecules will also easily enter your body through the skin unless
suitable protection is worn. Use the proper gloves and do the stripping
I use "JASCO Premium Paint and Epoxy Remover 15 minute." This is about the most powerful stripper that is "over the counter" available. It usually will take two applications. Although the first application will remove 95% of the paint, there's always a bit of residual paint that requires a second application. I use a razor blade-type scraper - a device that is designed for scraping dried paint off of glass. These work very well for removing the combination of stripper and old paint. Finish with running water from a hose and a wire brush to removal all stripper and old paint. >>>
| >>> It's common to find some rust hiding under the old original
paint. Most of the time this is a very minor problem and is from when
the cabinet was originally painted. It was obvious from the first
examination of E-50 that we would probably encounter more than the
normal amount of surface rust under the paint. See photos below showing
the rust on the panel and the rust on one corner of the cabinet lid.
This is "surface" rust and can easily be removed by sanding to bare
metal. When the new wrinkle finish is applied, nothing will show
through, even if the surface is not perfectly smooth.
After the rust is removed then the non-original holes have to filled. Bondo was used for all of the non-original holes in the cabinet. Since the "wrap-arounds" on the front panel had "notches" cut into them (from the rack mounting) a different method had to be used. Bondo would not be strong enough so these four "notches" were MIG welded to fill. The "finger lift" on the top lid had been "flattened" for rack mount clearance, so this was reshaped and then the small "relief" notches were lead-filled.
|photo left: The front panel after stripping showing the
surface rust that was lurking under the paint. This was caused by small
imperfections in the paint allowing moisture ingression to start the
corrosion process. The rust was deteriorating the metal which allowed
more paint openings which allowed more moisture,...on and on. This looks
worse than it really is. It can be easily removed by sanding and when
painted over with wrinkle finish, no surface defects will show.
photo right: This is some minor rust damage to the back right corner of the lid and to the back part of the cabinet. Again, this looks much worse than it really is. See photo below for this same area after painting.
|HRO Cabinet and
Panel Painting - The original black wrinkle finish used
on all early radio equipment was a two-part process that used a base
coat of Nitrocellulose Lacquer followed by a spray-on catalyst that was
heat-activated, usually requiring oven-baking to produce the finish.
Today, all we have available is a single-part process that can work
quite well if the proper conditions are provided for the wrinkling
First, one has to observe how the original cabinet and panel were painted. Since the base coat was smooth nitrocellulose lacquer, this will appear as gloss black. Note that all inside surfaces of the cabinet and panel are gloss while the outer surfaces are wrinkle. The outer surfaces was where the catalyst was sprayed. When baked to activate the catalyst, the result was gloss black on the inside and wrinkle finish on the exterior.
Before painting, wipe down all of the surfaces with lacquer thinner. This is to remove all grease, oil or other contaminates. To duplicate the original finish appearance, we first have to spray the gloss black lacquer on all of the inside surfaces of the cabinet, the lid support lips and the back of the front panel. On the removable front rail, spray gloss black on the inside surface and only on the lip that supports the lid. Let the gloss black lacquer dry overnight.
To do the wrinkle finish successfully you should only do one surface at a time. If you try to paint the entire external surface of the cabinet, you're sure to have a problem heating the entire paint job enough for the wrinkle to appear evenly. Before painting, I set up at least two heat lamps that are nothing more than 100W incandescent lamps with the aluminum bell reflectors as the primary heat source. I also have a handheld heat-gun to apply heat to specific zones that are the usual problem areas - like edges or corners. >>>
|>>> I apply the wrinkle paint in at least four heavy coats with
about one minute waiting time between each coat. Each coat is applied in
a different direction to avoid a "striped" pattern. Once the surface is
painted, it is placed it under the lamps. After about five minutes, I
start using the heat-gun to generally heat the entire surface but to
also heat areas that aren't receiving a lot of heat from the lamps. I
usually will apply the heat-gun from underneath of the painted surface
because too much heat directly onto the wrinkle paint will cause it to
"gloss" and not match the texture. I always keep the heat-gun moving to
keep the heat distributed and to avoid burning the paint. After a few
minutes, the wrinkle pattern will begin and then, using the heat-gun, I
apply heat just ahead of the pattern to move it along. The entire
surface should be wrinkled in about ten minutes total time.
Now, I move on to the next surface. At the edges, I shoot the paint from over the surface being painted rather than from the opposite side. That way the edges will blend and not have an "over lap" of paint that won't match correctly. When I do the top lid, I set it up so that the lid is down on the supporting lips. That way, the gloss black will be protected from the wrinkle finish and the end result will look like the original application did - see photo below.
The wrinkle finish is very, very soft at first so it's best to avoid any contact with the wrinkle finish "surface." I have to move the pieces carefully as I set up to shoot each side. When the painting is finished, I'll let all the pieces cool down for awhile. It's best to let everything set undisturbed for about one hour. After an hour, the wrinkle has set up enough to handle and move the pieces indoors but the wrinkle finish will take about two days to develop it's hard, durable surface. The longer it ages, the harder it gets. Avoid mounting anything to the wrinkle finished surface for at least two days.
|photo left: The cabinet and panel after painting
with VHT Hi-Temp Black Wrinkle Finish. Note that the hole for the
non-original pilot lamp has been filled. Additionally, the finger lift
has been reformed. Since E-50 was once mounted in a rack, the finger
lift had been "flattened" for rack clearance.
photo right: This is a close-up showing the detail of the lid support lips. Note that on the support section the paint is smooth gloss black while the top edge is wrinkle finish. Also note that the interior of the cabinet and the bottom of the lid are also gloss black.
|S-Meter Pearl Push-Button
- These were actually "door bell" push-button switches. They were
available with pearl, ivory, white or black buttons. I happened to have
a vintage ivory button type that had all of the nickel plating rubbed
off of the housing. I disassembled the switch to access just the button
part. See photo right for the parts that comprise the switch. I used
"Perfect Pearl" fingernail polish (Revlon) to paint on a "pearl" finish
to the ivory button. Then I nickel plated the housing. The finished
result is shown in the the photo below. The only thing is,...after I
finished the push button restoration, I found that you can still buy the
"pearl" push-button door bell switches for $3.49. I'm not sure if the
housing is nickel plated though,...it might be chrome. Also, they are,
of course, mail order,...minimum orders, shipping, etc.
Replicating the S-Meter - The S-meter that was installed in E-50 was a newer style S-meter, though not a Marion Electric type (even though it had that type of scale installed inside the meter.) The first thing to do was to find out what the original meter was. I really couldn't reference my 1935 HRO SN: H-103 because that S-meter is the early style HRO meter (run E used a meter type unique to that production run.) I asked my old collector friend, K6GLH, if he would take a close-up photo of the meter and button on his original "E production run" HRO and e-mail it to me. >>>
|>>> Gary's photo was very helpful for both the push-button and the
S-meter appearance. In looking through the various meters I had, I found
the exact meter type was also used in the RME-69 receiver. Luckily, I
had an RME-69 "parts set" that still had the "R" meter.
The next step was to replicate the National S-UNITS scale. I did have the correct meter scale photocopy that was used in the rebuilt meter used in HRO H-103. This was used as the basis for making a more accurate repro scale. The scale used in H-103 was printed on manila paper to give it the "aged look." Another more serious problem was the different location of the mounting holes between the two scales. This made a direct copy impossible since the holes would be obvious in the copy.
What was necessary was to first make a color copy of the H-103 meter scale on "photo paper." This type of paper is very white and somewhat heavier than regular paper. Then, I mixed Artist's Acrylic to match the background color of the meter scale in the copy and "paint out" the holes and add paint around the "meter action" cut-out since this didn't match the cut-out of the "RME" meter. When the touch-up paint was dry, this copy was then copied again using the gloss side of photo paper. The result was a meter scale that was slightly glossy but was "off-white" instead of manila and had the "aged look."
The new scale had to be glued to the brass backing of the meter scale. Alignment marks must be used along with pre-punching the mounting holes so the finished scale will be "straight" when mounted. When the glue had set-up, a razor blade was used to trim the excess paper to the exact size of the metal backing plate. This was then mounted to the meter using the original acorn nut hardware. The finished result can be seen in the photo to the left, which also shows the finished pearl push-button.
Nickel Plating the PW-D and other Parts
|How to Nickel
Electroplate - This is just a brief description of the
process. There are full instruction pamphlets available where the nickel
plating supplies are purchased.
Electroplating requires a power supply, a variable load resistor, a pure Nickel anode and a solution of Nickel Sulfide. The Nickel anode is connected to the positive terminal of the power supply. If the power supply is adjustable, you won't need the adjustable load resistor. If your power supply has a fixed voltage level output, then the adjustable load resistor allows you to adjust the current for the proper plating results. Your pure Nickel anode can be purchased from hobby-amateur jewelry stores that usually carry many types of electroplating supplies for the amateur jewelry maker. They will also have the Nickel Sulfide solution, usually available in quart plastic bottles. Note that the anode is riveted to a stainless steel holder. Stainless Steel will not "poison" the solution and ruin the plating results. Your piece to be electroplated is called the "cathode" or the negative connection. The conducting medium is the liquid Nickel Sulfide solution.
The item to be plated must be brass or copper. Aluminum and other similar metals can also be plated with the Sulfide solution. Steel must be copper plated first before Nickel plated. If you try to plate steel directly, it will turn black. Next, the item must ultra-clean. You can use any de-greaser or an etcher-cleaner like Sparex. If the item to be plated is a "rough" surface then that will show through the plating resulting in a flat, coarse appearance. Be sure the item is either polished or smoothed to the desired finish before cleaning and plating. The item to be plated must be held with wire or clips that are made of copper, brass or stainless steel. >>>
|>>> To set up, use wires to connect the Nickel anode to the
positive terminal of the power supply with a variable series load
resistor if necessary. Place the Nickel anode in the Nickel Sulfide
solution so that just the pure anode itself is submerged in the
solution. The solution should be in a non-conductive container, like a
plastic bowl. Connect the power supply negative terminal to the piece to
be plated using an "alligator clip" that is made of copper. Be sure the
power supply voltage is as low as possible, less than one volt. Place
the piece (cathode) into the solution and be sure the entire surface is
submerged. Now, slowly increase the voltage (which increases current
flow through the solution) while watching the anode. You will begin to
see small bubbles coming off of the anode as the voltage is increased.
You should not increase the voltage any higher after you start to see
bubbles coming off of the anode at about the rate of the bubbles seen in
a glass of champagne. If the anode "foams" you have the voltage way too
high. Too high of voltage/current will cause the plating to turn black
almost immediately. Start at a low voltage - electroplating doesn't
require a high voltage at all, usually only two or three volts works
fine. Watch the bubbles and your plating will turn out fine. It only
takes a few seconds for the Nickel color to appear on the item but it
takes several minutes for the plating to attain a good thickness that
will be durable. More time equals a thicker plating. Usually small items
take about five minutes while large items (2 to 4 inches diameter) might
take 20 minutes. If you increase the current to speed up the plating,
you run the risk of the nickel plating turning black. Keep the voltage
and the current low to assure a good bright finish.
If you're plating screws, you can do several at a time by just looping the wire that is used to hold and immerse the items and then use an alligator clip to connect to the wire. On large items, two anodes can be used to increase the capability of the set-up. Do not allow the anode and the items being plated to touch. They should be about an inch or so apart. It depends on the size of the item being plated and the number of anodes used. Rinse the plated items in water and then they are ready to use. No polishing should be necessary. Remember, you can usually buy full instruction booklets along with the plating supplies at the hobby amateur jewelry store.
NOTE: A small amount of gas is given off in the electroplating process (the bubbles you see in the solution.) It can cause headaches or even nausea if the electroplating is done in an enclosed area. Be sure you perform the electroplating process outside or in a well-ventilated area.
|Nickel Plating the PW-D
- To accomplish recreating the nickel-plated PW-D required stripping the
paint from a later style PW-D with the lacquer finish. Be sure when
selecting the later style PW-D that it is one that still has only one
set screw with the matching one set screw HRK knob. Many of the PW-Ds
found surplus today are WWII types (and later) with two set screws. To
match the nickel-plating, the PW-D should be the earlier style. The
paint is easily removed with JASCO Paint & Epoxy Stripper leaving the
index dial and the number dial looking as shown in the photo to the
right. The white index line fill has to physically be removed with a
sharp tool because it is non-responsive to JASCO.
Note in the photo to the right that the Number dial is very rough finish, especially in the number scale area. The Index dial casting is pretty good but still isn't as fine of finish as the earlier "plated" dials were. Since we're stuck with using "painted" dials we will have to see how well they will electroplate. It took three attempts to get the Index dial to look fairly close to an original dial. The first plating was very dark due to excessive current in the set-up. The next attempt was also not satisfactory due to a very "splotchy" appearance. >>>
|>>> For the third attempt I reduced the current to a very low level
and this resulted in a fairly even, close to the "original color"
plating job. I think if I could have copper plated the Index dial first,
I would have had better results. Unfortunately, copper plating requires
the use of cyanide in the liquid solution, so I just settled for the
"close to original" look. The Number dial, being a "rough" casting, was
difficult to get the finished plating to be consistent and without pits.
Since this was a painted Number dial originally, I believe that National
allowed the dial manufacturer (Doehler) to use much "rougher" castings
since they were going to be painted anyway and the paint would act as a
The end result for the nickel-plated PW-D was that the finished quality was not as high as I would have hoped for. It's difficult to recreate the exact finish with "hobby-type" equipment and processes. Also, since this was originally a "painted dial" I'm not sure that the material used for the castings was exactly the same as the earlier "plated dials." Additionally, I was using a pure Nickel anode which probably wasn't what the original manufacturer used. The upshot is I'll be looking for an original "German Silver" PW-D to match up with E-50 correctly.
photo left: E-50 is coming together. Front panel installed. Ready for wiring and component restoration.
Capacitors - Nearly all of the paper capacitors in E-50
were replacements that had been installed over the past years. National
used Sprague capacitors in all pre-WWII HRO receivers and,
unfortunately, all of the replacements were not Sprague but were
Aerovox, Philco and other assorted brands. I "harvested" almost all of
the required Sprague caps from a "parts set" NC-200 receiver that was in
the junk box. I had some other Sprague caps in the "capacitor box."
Well, that's what I thought before I was lucky enough to acquire HRO D-65, a very original first production run receiver. Under D-65's chassis are 15 Micamold caps. E-50 has five Micamolds. I seems likely that Micamolds are original to the early HROs. Certainly, later HROs will have Sprague but apparently not the first few production runs. So, recreating the orange Micamold look is something we will have to develop a method for since these style of Micamolds are seldom encountered.
So, why all the fuss about having the proper manufacturer capacitor when you're going to replace the capacitor insides anyway? Attention to detail is what makes a "museum quality" restoration and having the correct types of capacitors is an important detail. Many restorers don't care what is under the chassis and will rebuilt a receiver circuit using modern equivalent components installed "as-is." Their motto is: "As long as it works!" Well, with "museum quality" restorations, not only does it have to function correctly, it must look original, too. Therefore, not only are the correct capacitor shells used for rebuilding the capacitors but each new capacitor is inserted into the shell oriented to agree with the outer foil band on the shell and is installed into the circuit with the correct orientation of the band as per original.
|We use modern
polystyrene dielectric film capacitors commonly called "Yellow Jackets."
These are self-healing capacitors that are small enough to fit into the
original paper cap shell. These capacitors are probably a thousand times
better in quality than the originals and, since they are self-healing,
they won't develop leakage current problems.
The re-stuffing procedure is to use a heat-gun to melt the wax holding the original capacitor in the paper shell. After the wax is hot enough, use needle-nose pliers to grip one of the leads and another needle-nose griping edge of the shell. Pull gently and the insides should come right out leaving just the paper shell. Wipe the shell off with a paper towel to remove the old wax and dirt. What you're left with is a nice condition, clean capacitor shell.
Now, orient your poly-film cap so that when the nomenclature of the cap is upright then the foil side will be the left lead. It doesn't really matter with film caps which is why there is no band on the cap body but I always install them with the left lead as the outside foil. Use a small amount of hot-melt glue to secure the poly-film cap and let that set-up (a few minutes.) Now, fill each end of the shell with brown colored wax. Don't use bee's wax as its melting point is too low for this application. Sealing wax works better. After the wax has set-up, the cap is ready to install.
I normally rebuild each cap as I go through the circuit as there will be no confusion as to how the original cap was mounted. However, E-50 was missing its original caps and this allowed us to collect the correct types and rebuild them all in advance of installation. This saves just a little bit of time in the overall process but it does require more planning so that the rebuilt caps are installed correctly. For this restoration I was able to reference HRO H-103 as a model which saved a considerable amount of research that would have been necessary for correctly installing the capacitors.
|Making Lead-End Resistors - This process was detailed in the restoration of HRO H-103. Here it is again,... Another challenge were the white ceramic resistors with lead end-caps that National used in the HRO receivers up to about mid-1936. I had to "recreate" three of these resistors to replace modern resistors that had been installed. I checked the parts boxes and found three correct size lead end-cap resistors. Of course, they weren't the correct value but all we needed were the lead end-caps to build our replicas. Next, I needed to find correct value, IRC (International Resistance Corp.)1/2 Watt Carbon resistors from the late thirties. These resistors are the correct physical size to fit into the lead end-caps. The lead end-caps will just "twist off" of the old resistors and then, by drilling a 1/16" hole, the lead end-caps can be fit onto the new resistor (with the leads protruding through the holes.) Soldering secures good electrical contact to the lead ends. All that remains is to paint the body white and install the resistor replica. Originally, the ceramic resistors were lettered by hand or stamped with the value, however it looks better to just leave the body white as nothing looks quite "correct" or "original" for putting the value on the resistor. The photo to the right shows one of the replicas installed next to a rebuilt (restuffed) paper-wax capacitor.|
Switches - I ordered one of the doorbell switches that
were made by Philmore to see how they look. If it looks better than my
"Revlon" version, I'll use it instead.
UPDATE: The Philmore doorbell switches are not useable because the button surface is "convex" instead of "flat" like the originals.
|PW-D Plating, Again - In an attempt to "dull" the nickel plating and maybe "even out" the look of the PW-D, I dipped the outer dial in a dilute solution of H2SO4. This rapidly showed me that I hadn't left the PW-D in the nickel solution long enough because there was very little nickel on the dial. The base metal of the dial reacts quickly to the acid while nickel reacts very slowly. Since the base metal turned dark gray, it was easy to see that most of the dial wasn't plated. The next step is to re-plate the dial but this time use nickel coins for the anode. Nickel coins are actually nickel and copper which is close to German Silver. Additionally, the dial will be left in the electro-plate solution for at least 20 minutes to allow full plating. Since an original plated PW-D seems to be made of "unobtainium" we are going back to trying to replicate the early style PW-D.|
photo above: E-50 as of January 3, 2012. Shaping up pretty well
|White Graph B Coil
- I was able to build up an early version B coil thanks to the
acquisition of D-65 with its matched coils. I was able to copy all of
the white background graphs from D-65's coils. I had the coil assemblies
for an early B coil set, all with the small contact buttons typical of
the D and E run HROs. I had a thick panel with wrinkle finish left over
from the F coil that came with E-50 (those F coil assemblies were
mounted to the correct type steel panel to build up an F coil set for my
HRO-W.) After assembling all of the early style parts, I now have a
complete white graph B coil to go with the white graph C coil for E-50.
The Final TWO "Missing" Parts Acquisitions - I still need to find a nice condition early style PW-D micrometer dial for E-50. Also, the RF GAIN dial that came with the receiver is from a later HRO and we are still looking for the early style, short-boss RF GAIN dial.
Thanks for the Parts - Thanks to Scott KA9P for the small pointer knob for the Selectivity control. Thanks to Bill Fizette W2DGB for the two National ceramic tube sockets needed. Thanks to Jim Allen NU6AM for the small red "NC" pointer mounting screw.
Paper Capacitor Update - A thorough examination of HRO D-65 has lead me to believe that all early HRO receivers came with Micamold brand paper caps. D-65 has 15 Micamolds with the remaining 6 caps being five Sprague and one Tobe. E-50 has 5 Micamolds remaining but E-50 has an extensive repair history. It's unlikely that so many Micamolds would turn up in two different HROs unless they were original caps. Sprague was the OEM after the first few production runs. This will require a method of recreating the orange paper label of the Micamold caps in order for E-50 to have the correct under the chassis appearance.
To be continued,...
The restoration of E-50 will be added to this article as the work progresses. Check back often. - H. Rogers, Latest update - May 10, 2012
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