Good news everyone! I recently acquired another original early model radio 986067 for 1947-1950 AD trucks. (it will fit to the 1953 for sure, and maybe the 54? i don't know the details of 54-55 radios)
This radio is the most complete original I have to date, it's not the best shape, however it is mostly all there with exception of the broken knobs. All the tubes inside are labeled GM Genuine parts
I'll post more photos as i fix it up. Please send questions and comments -stan
I think you have a nice radio there, it seems to be complete, congratulations. I hardly see any for sale these days. It has one of the original type speakers that they used to call elctrodynamic.
hi truckernix, yes i found the part number on the speaker and it matches the parts list: 7255903 Electro Dynamic 6-3/8 x 9-1/4 Elliptical working on my last radio i was fortunate to source this same speaker part number from someone up in Oregon
attached are more photos of the speaker and some tube testing (all good!, but you have to push the big red button for test, so ignore that the needle is in the "replace" area in the photo)
unfortunately the electrolytic capacitor was much too gone, overnight it was not showing any signs of healing, the leakage was much too high and i hadn't reached anywhere near usable voltages. so like others online suggested, i opened it up and stuff it with modern parts , at least it looks okay and it's a convenient place to put the new caps because they would get a bit in the way on the underside -s
for the sake of authenticity, i'm going to reuse the mechanical vibrator in this radio not surprising it did not test good but i've fixed these before, this time i'll try to be a bit more gentile with the parts so it doesn't look so bad when i'm done.
vibrator delco part number 7239124 = 6V, 1-1/2 x 3-1/8 inches, Frequency 105-110 Hz, 6 Amps max. load
photos of disassembly attached, going to clean up all the parts and do the contact points with some wet stone and sandpaper, some articles state to never use "emery" pad or cloth on these kinds of contact points (similar for voltage regulators and such), a file is okay
the idea being that emery will leave behind microscopic particles embedded in the surface, sure it will work but longevity tests result in shorter time to failure dunno any more details, but the wet sandpaper is handy and does a nice job, seems to me sandpaper should be as bad as emery cloth then, but maybe the aluminum oxide grit is okay compared to diamond grit. -s
The issue with using abrasives to clean the points is that the embedded particles can cause the points to stick. If the points are flat, a very fine cut point file is OK, especially if there is evidence of burning - nothing to lose. If the points are rounded, as they are in voltage regulators, DELCO recommended only a spoon or riffler file (the type of file used by silversmiths) be used, since the flat file can't conform to the point shape. If some of the points look pretty good, and just need burnishing, then a file probably isn't needed, just some stiff card stock or something like that. Hope this helps!
I should add - I'm following this with interest, as I have been contemplating giving a go at restoring an original radio in my '53. Thanks!
vibrator completed, i cleaned the points with wet sand paper and water, then i polished them to try to get all the grit out even tho you can't see or feel it hope it worked photos attached of one point, before and after side by side, the all looked that bad.
i cleaned the can off with a bit of toilet bowl cleaner to freshen up the zinc plating without removing the red ink
the gaps are set to about 3-4 thousands of an inch, photo taken before fine tuning them ideally the on-off time would be 50-50 but that would mean a gap of 0 which isn't possible with this design because then the contraption wouldn't start oscillating
the armature must clear the coil post by at least 5-10 thousands of an inch, if it is too close even not rubbing it leads to sporadic oscillations, i was getting a beat frequency where the armature was going back and forth between spending more time on one contact then the other at about 1 Hz rate, i finally figured out the solution after an hour of readjusting the points with no success
i used an oscilloscope to look at the duty cycle and frequency, it's not the most accurate tool for measuring frequency but for the application good enough. i did many start up cycles and a short burn-in before crimping it up, then an hour run post crimping. this vibrator is running exceptionally quiet and smooth
next step gonna look at getting the main chassis cleaned up and sourcing some replacement parts -s
Wow that is impressive. I keep a mechanical vibrator handy for when I first try out a rebuilt radio. The solid state ones don't stand up to a power supply short very well!
Very nice 2Many' ! By the looks of the "before" points, you didn't have much to lose, and polishing should work, I would think. It's probably running better now than when new! Nice!
this week i didn't get much done, went to Surplus City in Albuquerque NM and was rummaging in the back again, found some 6 volt vibrators for parts ($2 each) mine will likely need new points next time it fails. they also have a nice selection of electrolytics for tube equipment
i got the radio chassis stripped of all it's parts, only steel remains, the zinc plating is corroded through to the thin copper flash over steel in some places i'll look at getting it and some other parts re-plated with fresh zinc in Oakland this week this shape has too many intricate inside corners to plate well with the home-brew vinegar plating technique, flats and outsides plate okay but my experience is too limited to successfully getting inside corners to plate at all -s
update on radio fun, this morning i drove some of the steel chassis innards to the sandblasting / plating shops up in Oakland
started some cleanup work on the tuner unit used Meguiar's ultimate polish to clean the dial face, i think it turned out very well some parts had received a good layer of blue paint, i'm going to reuse the plastic part of the escutcheon because the aftermarket replacements don't allow an original dial face to fit. (i find that in general reproduction plastic escutcheons won't fit most of the parts that need to go into them)
after carefully scraping off the paint and sun damaged parts, i was able to use boiling water to carefully straighten and restore the form of the original plastic i'll repaint it with a wine/maroon color, it's not original to have paint, but it's in too rough of shape and color anyway anyone wanting a more precise restoration would either have to work with the aftermarket plastics or use a better matched paint on this one repainting this part would not require much effort -s
i don't have any cleaning apparatus, so far i have been using evapo-rust, soap, rubbing alcohol and manual labor. i have though about getting some sort of small bench top device, would ultrasonic baths clean off surface rust? is it like a fancy rock tumbler? i will go google this, i've thought about it before and i do have a couple dozen screws that need cleaning or replacement
I haven't used one either. I think jewelers use them and hobby stores are selling them these days. That product Evaporust is amazing stuff. It attacks rust and leaves the other metals alone.
I did some googling, and watched some YouTube about these ultrasonic cleaners, some folks swear they can remove rust with reasonable results with the correct cleaning solution Based on what I saw on YouTube it should be a useful tool for cleaning dirt and grease at the very least, so I ordered one from amazon for under 100 It will arrive in a few days and I’ll post how well this China machine does. -s
progress... refurbishing the power/volume/tone switch took it apart, cleaned all the bits, put a bit of fresh zinc onto some of the parts, re-assembled
the brass is stained because the oxidization reduced the alloy to just copper at the surface in some places not sure the best way to make it look brass again, if i had a very fine wire brush i could probably polish until i'm at brass again but it's in the bottom of the threads suggestions? -s
Maybe try Flitz polish on the brass? Will take some work to get down into the threads, but it works well to polish brass (among other things). I first used it when I was working as an electronics tech in grad school, to polish the internals (brass tubing) of an electron beam column in what would now be considered an antique scanning electron beam microscope. It was the only thing that allowed us to keep the internal structure clean enough to keep the beam focused, FWIW. Basically removes oxidation and leaves no significant residue if wiped off thoroughly. We used isopropyl alcohol for that. Nothing very exotic...
i found some compounding paste and used a fine steel wire brush, the brass got reasonably better
also i got an ultrasonic cleaner on amazon, gonna test it out soon on some intricate tuner unit parts in the mean while, please enjoy the tuner coil before and after photos
the center double coil halves had broken free from each they should be glued together so they can't move i ended up rewinding the coil after all the brittle gyptal flaked off and the windings came loose -s
the ultrasonic cleaner... it works okay, but it won't remove everything it did a reasonable job of this complicated part in the tuner unit, photos attached i used only water and a bit of shampoo in the cleaning bath
i have two of this particular assembly, the other one is brighter and better looking, probably will go with the other one
maybe i should try baking soda or some stronger chemicals in the bath, i heard folks use evapo-rust directly in the cleaning bath -s
By my experience, ultrasonic cleaners work great with weak solvents (isopropyl alcohol, methanol, that type of thing) for degreasing. Detergent solutions are fine, but with anything that is more aggressive, be cautious. They start etching pretty fast with mild to stronger acids, like evapo-rust. If you try those, go with short cleaning times initially, until you see how a particular solvent behaves with the parts that are being cleaned.
hi truckernix, it isn't too difficult, as long as you make it look close to what it was like, it will be fine, because later when we go through the alignment procedures any small variation in the coil winding will be calibrated out.
in the photo of the dirty coils in the vise, the center outer portion is dropped down a bit, and touching it i could see it was sloppy loose which is no good on rough roads to the listener a weak station could have loudness variations with truck motion as this coil giggles, but it would likely not move enough in one instance to notice, really it just needed to be fixed on principle
the circuit of what this coil does is attached as well - the two halves are for the variable oscillator that modulate the selected band to the IF frequency. the oscillator must be able to span frequency ranges of (535KHx - 262Khz) to (1605KHz - 262KHz), that's 273KHz - 1343KHz to keep the range overlapping properly with the selected station, the span offset is taken up by adjusting the iron core positions relative to each other it's a pretty neat Rube Goldberg machine, but it works repeatably.
once removed from the rubber holder grommet, i slipped the coil apart into it's two halves, the inner one is a solid winding 1 layer thick end to end, i only had to re-wrap about a half dozen turns at each end and then held it in place with painters tape while the wax was warming up the outer half i tried preserving the coil but soon it all fell apart, since it's only 15 - 1/4 turns of evenly spaced wire, i decided pulling it all off and re-wrapping it was easier than trying to re-melt the gyptal in place, the spacing is not super critical as long as nothing moves when we are done that's what's important if one wrap is closer or father apart it will have virtually no significance to the desired mutual inductance of the inner-outer coils because the gap is so large between the two and it's an air core.
i taped the wire at one end close to where it was at before (you could see a shadow of the old wire on the core) then i rolled it on the table top, 15 turns happens fast, so go slow and even then tape the other end up. put a dab of wax here and there to hold it all together then i followed up with a bit of rubber cement in a strip along the wax (not shown) and finally used a hot air gun to remelt the wax evenly once the rubber cement strip was holding
wax is a good intermediate holding solution because it's very easy to undo if something goes wrong before you commit with the rubber cement -s
update still waiting on the plating shop, so in the mean while, here are some photos of the tuning clutch getting a new rubber pad for this task i used part of an inner tube, sanded it smooth then glued it to the assembly with contact cement, you can't use rubber cement for this task (i tried), rubber cement only seems to work when it's rubber to rubber, it peels off the aluminum very clean and easy contact cement seems to hold more like original
the clutch serves two purposes in the tuning assembly, one is to allow the tuning knob to slip if you try to turn it past the end of the mechanism limits, the knob is worm gear driven so you would have insufficient feedback before things got a lot of forces applied the second purpose is that it has a dis-engagement lever used when any of the tuning buttons are depressed, the first part of travel of a button opens the clutch before the final travel meets with two parallel rods to swing the tuning core guide bar.
for interest sake i included a photo of three button assemblies side by side with with different parts of the AM band programmed into them this is where the "memory" of a tuned station is stored in the radio these buttons have both ends and the center of the AM band stored via the half round disk that can swing to any angle. when a button is pulled out, that tiny disk can float free, as you push it back in, it hugs the two parallel tuning bars that rotate around a mid point the disk rotates to match the position of the two parallel bars perfectly as you press the button back in for programming, then on final travel of the programming action a lever pinches this half disk to clamp it firmly into position to remember the station.
Hi truckernix, yes if someone wants to save the info or make an article out if it that’s fine by me, I think that would be neat. I’ll answer any questions the best I can, also I’ll take advice too, i know I’m not going for perfection most days, but I’m trying the best I can with the motivation I got. -s
finally got some parts back from the hot dip galvanizing the original zinc was likely electroplated on, but i decided to take a risk and see how hot dip would turn out on some thicker steel parts
the zinc is quite thick in some places, i have spare parts of most of these pieces so later i can rework them and decide which way to go the hot dip process is a bit rough on the smallest parts, i see it did damage the light reflector part, fortunately it is not the one from the radio it was a spare that i was ready to sacrifice for the cause... so now i know better
there may not be updates for a little while now, got to make progress on spring outdoor things but i will return to it, feel free to send questions as usual -s
I was away for a while working on other projects, but i did make a bit of progress on the radio. while being near the gas welder, i fixed the radio housing. i wanted to see if i could weld it reasonably okay without totally destroying it. now that i have something that might be usable i'll spend time cleaning it up, i'll likely fill in the remaining imperfections with epoxy.
attached photos of the rusted / broken dimples that hold one end of the housing together notice one slot was stamped a bit too close to the edge and rotted open i managed to make a new dimples and welded patches with fresh dimples in, the radio housing is 0.040 thick, i couldn't find material in that thickness in all my junk, so 0.035 got used.
this weld mess of mine can always be cut out and redone if a better radio housing cannot be located in the future it will be our secret for now -s
Here is the latest progress. I have been taking advantage of summer to do outdoor things, haven't given up on the radio.
I put the tuner unit back together yesterday and today. Overall my method is: take it apart as much as i can, clean everything up, re-assemble with as many original parts as possible but don't go overboard using old parts if they are not good enough.
So turns out that hot zinc dip was probably not the best idea. Many threaded holes and tight clearances needed to be cleaned up to fit, that took a lot of time with files and sand paper and thread chasers. The movement should operate easily without any oil when all the parts are clean. Once it's together you do oil it and then it really gets smooth.
There was a lot of taking it apart to re-assemble in a different order. I should have made a few more notes about the disassembly order.
I am posting only photos from the successful order-of-assembly path. This means i have a fewer images to share, but on the plus side, when you look at any of my photos you will see a partially assembled state that should not require any disassembly if you reproduce that specific state during your work.
Attached photos: - tuner unit chassis - how to compare button return springs, I discovered that the earliest versions of this radio used substantially weaker button return springs. - weak spring vs newer stiffer spring, my springs got mixed up, but putting them back to back we can clearly see a difference in compression. - installing the buttons, us an alligator clip to temporarily hold them in place - all buttons installed
The button retaining part had a soft rubber strip on it that cushions the buttons return and prevents rattling on metal. I have replaced it with adhesive felt. It is a bit difficult to see in the photo, but there is a felt on both edges of that retaining part that the buttons extend through.
When using non-automotive grade self adhesive felt, i go around the edges with a dab of crazy glue to ensure the low quality adhesive won't let go.
second post with more pictures to follow shortly -s
- coils with iron cores installed - soldering the antenna wire braid back like it was, half on the chassis and half on the coil can - the old wires used as reference when making new wire bundles - soldering the power wire braid onto the tuner unit, this is also where the dial indicator ground wire solders, it seems redundant but the radio originally has this ground wire. - complete tuner unit with all new wire bundles ready to go.
hope i can get back to the radio sooner next time, next thing i'll work on is the dial face. -s
update painted some of the dial face parts, there are a surprising many bits to just the dial face on these radios some of the parts were two colors, black to minimize light leakage and the dial face color sorta sandy tan i use the closest colors from rustoleum brand spray that match the old paint alright, i'm not sure if the remaining paint is even the correct color after 70 years, as long as colors go well together and it looks good to my eye is what i care about right now.
to top indented edge of the clear dial face is white to reflect light around the top edge down onto the numbers, it acts like a 90 degree light pipe a bit. reproduction dial faces do not come painted, and their numbers are just a low quality sticker so they won't even light up 3D like an original. -s
update, got a first coat of Maroon on the Escutcheon assembly plastic body, i used maroon because it's a bright lovely color but in line with the spirit of the original purple plastic color used for knobs in these old trucks. painting this plastic allows me to color match it to the control bushings behind the knobs, it protects the plastic from further UV damage, and covers up existing damage allowing me to reuse the original. i also painted a reproduction escutcheon to see if i like that one more when i'm doing the final fit.
The steel housing is ready for paint, i'm going to paint it inside and out, originally it was not painted inside. I masked off a few places where i want metal to metal contact with the guts later on. if i had a better housing i would not use this one, it's in bad shape, i suspect it was left outdoors for decades. i cleaned it up, straightened it up and fixed some of the damage on it the best i could, hopefully it will turn out well. -s
hi everyone, here is an update on my radio project, now that fall outdoor activities have ended i can resume working on my inside stuff.
i painted the housing Rust-Oleum Brown (210880 Hammered Metal Finish), i was gonna use the copper hammered finish but it seemed a bit too bright this brown looks very satisfactory for me. photos attached showing the masked areas and how it turned out, paint really does hid the many imperfections
i may wait to glue on the reproduction decals until i'm ready for final assembly that way I don't damage them when i invariably have to take something apart many times to make assembly corrections.
All the misc. riveted bits go into the chassis at this stage, I don't want to be driving rivets home when there are electrical parts or transformers installed later on.
Cleaned up the excess zinc plating on the holes and edges of the chassis. The vibrator clamp will be replaced as it has broken tabs. The new one will be riveted with tiny steel rivets in place of the spot welds in addition to the socket rivets which go through the clamp, chassis and socket. I would not recommend dip galvanizing, it's a pain and not original. It would be better to spend more time getting the electroplating to work out as it was originally done, but getting the inside corners to plate is difficult. I will live with this learning experience for now on this radio.
I riveted the tube sockets back in using my handy small engine valve clamped into my table top vise. Some insulating papers were not the best shape, i found a very similar cardboard at my local junk store in San Jose Cali. If anyone is near the bay area, check out Excess Solutions, you will spend a whole day rummaging around
One of the wires had broken off the audio transformer, the remaining were not looking good. Carefully took the transformer apart to solder intermediate 30 gauge wires onto the tiny input side windings, these wires are in turn soldered to the larger wires that exit the transformer.
I used friction tape to wrap the transformer, it can be locked in place by applying cyanoacrylate to the tape ends. Once installed onto the chassis it is soldered in place on it's folding tabs. There are only 3 wires on the audio transformer because one side of output is tied to chassis ground. The speaker plug will return speaker current back to chassis ground at the speaker plug.
While soldering big stuff with the propane torch I also installed the triple electrolytic capacitor. The capacitor body is the common terminal of the electrolytic. At lease one mounting tab must be soldered to the chassis to ensure a good connection to ground. I often use tinfoil as a heat shield when soldering this way, the torch will quickly burn things or cause discolorations if not contained.
The power transformer also gets one edge soldered to the main chassis. The center tap of the input side of the power transformer is tied to chassis ground internally; this soldering is necessary to ensure the best performance from the power stage.
update Without burning my fingers... i have managed to install all the main chassis components. It's starting to look like a radio again!
Put fresh wire on the I.F. transformers, the old wire was faded and very oxidized internally. The painters tape is to protect the parts during assembly. I used colorful red shrink tube on the component leads in place of the original black cloth tubing which has all gone hard, i like the new red look, if someone prefers black that's easy too.
Most of the new resistors are now metal film type which are more stable and lower noise than the original carbon composites; these are likely overkill for this application, but the absolute price difference is not significant so why not splurge (pennies) on better parts right?
The large circuit capacitors are mostly PP or PET types that I got at the local junk store. As long as they have the correct value and sufficient voltage ratings that's all that matters for the most part. All trimmer mica caps are original, they will outlive modern civilization. I did disassemble some partially to clean them, but that was not electrically necessary, cosmetic only.
A sharp eye will notice i added a capacitor across the vibrator pins and also two on the main power input under the power transformer. The vibrator capacitor will help save the points inside the vibrator, this capacitor is standard on the next generation radios that came after this design. The bulk capacitors are to help with incoming noise from the vehicle. These locations likely would have had a capacitor when the radio was designed, and then they were omitted along with other parts we will never know about in order to reduce cost. -s
Now that the main chassis and tuner unit are complete, i will require a speaker to connect to them when i do the alignment. So it is time to tackle the speaker.
This radio came with an original electro-dynamic speaker, part number 7255903, this one is completely rotten and frozen with rust and dirt. A side note - There is some evidence that later on these radios came with a PM (permanent magnet) speaker. If you find a PM speaker (possibly part 7256355?) in your radio it could be the original too. If the pole magnet is too weak you can order a replacement magnet when rebuilding a PM speaker.
After carefully extracting the voice coil (because i might reuse it), I pressed out the pole piece. It presses out relatively easily from the back side towards the front while supporting the top plate with a large socket or pipe. Once the pole is out, the field coil slides out with the cardboard shims and the copper plate. I am not certain about the thick copper plates purpose. Either is is just a gap filler or the designers were getting fancy and thought this plate could be a 1 winding shunt for any AC ripple current presented to the field coil. Either way, it will be going back in, it's 1/16 thick and is needed to keep the field coil tight.
The original voice coil seems re-usable, however the paper may continue to warp so i will order a new one and decide which to Using paper shims to fit the original voice coil snug onto the pole I measured it's ID. (this way i know it's round and not oval) I will order a new mylar backed 1.000 ID voice coil which is probably what this original coil is suppose to be.
The spider cup needs to be about 2.2 inches in OD and about 0.2 inches high. The closest size to get is 2.171 OD x 0.197 height, I prefer to go the nearest size too small, as anything too big just never fits well and flat.
For anyone else who is rebuilding new or old speakers, my source for parts is The Speaker Exchange https://reconingspeakers.com The next post will be re-assembling the speaker, and i will include the specific part numbers for the replacement parts used. -stan
speaker assembly follow up, i'll make two post today so i can put up more photos
material list: original speaker parts all cleaned up Devcon 18045 contact cement Devcon 20445 5min 2 part epoxy VC3000-4 - mylar/paper voice coil 1.000 ID, 4 ohms CS2171-C - spider cup 2.171 OD, 1 inch VC, 0.197 height W438001 - 6x9 cone DCP1100 - 1 inch dust cap (1.100" with down lip) R6X9 - mounting gasket for standard 6x9 PIGTAIL and SHIM KIT - included with most orders from the Speaker Exchange, these are the super flexible lead wires from the voice coil to the speaker terminals, and the shim kit has plastic card stock of various thicknesses to use instead of paper when spacing the voice coil onto the post.
The Speaker Exchange website has a good DIY section with photos on how to rebuild speakers. I had no idea how to rebuild speakers before a couple years ago, i just knew it was a thing that could be done, I've followed their guides and so far they all turned out great. https://reconingspeakers.com/faq/how-to-guides-2/ ……..How To DIY Recone with Unassembled Parts — most brand parts
What's specific to these Electro-Dynamic speakers is mostly the details of the field coil. I used more of the black friction tape as i did on the speaker transformer to wrap the field coil where it had lost the crumbling paper wrapping. Glue the ends of the tape with cyanoacrylate to keep it from unwrapping. The field coil slides in with it's copper plate and cardboard shims, then you press the steel pole piece back in from the front side of the speaker. The pole originally was a few thousands of an inch proud of the rear side, to get it there I first press it flush on the steel bed of the arbor press. Then the tricky parts comes in, the pole gap must be uniform, so measure it with a round rod/drill bit or any measuring stick of choice to check for uniformity. Assuming it's not prefect by luck this next step is how you center it and get the pole driven a tiny bit further into position.
With solid cardboard or leather supporting the speaker use a 1/4 inch steel punch and tap off center on the pole next to where the gap is largest. This action drifts the pole closer to the side you are tapping off center, closing the gap next to the punch (and opening the gap on the opposite side). Tap a bit and measure often, eventually you will get the hang of it and the pole piece will be reasonably centered. If it all goes bad, press it out and start again. If the pole is too loose, put a few dimples on the end that presses in and start again. There should be virtually no limits to how many times you can repeat this step to get it right.
Always test fit the parts before attempting glue or epoxy. The DIY guides cover the order of assembly quite well, but if you are not certain, plan it out yourself so that you know how all the steps will go before you start. I like to go slow, I leave the glue and epoxy cure overnight for a couple of the assembly steps. -stan
