Excellent, another radio to play with

Posted By: 2ManyTrucks

Excellent, another radio to play with - Thu Mar 28 2019 08:24 PM

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 smile

I'll post more photos as i fix it up. Please send questions and comments

Attached picture radio.jpg
Attached picture radio_side.jpg
Attached picture radio_tubes.jpg
Attached picture radio_guts.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Thu Mar 28 2019 09:42 PM

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.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Mon Apr 01 2019 08:14 PM

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

Attached picture speaker_7255903.jpg
Attached picture tube_test.jpg
Attached picture capacitor_reform.jpg
Attached picture capacitor_refill.jpg
Attached picture capacitor_assembled.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Mon Apr 01 2019 08:32 PM

They eventually switched to a modern type speaker. They work just as well. It looks like you are having fun!
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Wed Apr 03 2019 09:53 PM

update on the radio

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.

Attached picture vibe_test.jpg
Attached picture vibe_open.jpg
Attached picture vibe_inside.jpg
Attached picture vibe_parts.jpg
Attached picture vibrator_7239124.jpg
Posted By: drdoug

Re: Excellent, another radio to play with - Wed Apr 03 2019 10:08 PM

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!
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Fri Apr 05 2019 04:58 PM

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 smile

next step gonna look at getting the main chassis cleaned up and sourcing some replacement parts

Attached picture vibe_points.jpg
Attached picture vibe_clean.jpg
Attached picture vibe_gaps.jpg
Attached picture vide_adj.jpg
Attached picture vibe_pass.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Fri Apr 05 2019 06:40 PM

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!
Posted By: drdoug

Re: Excellent, another radio to play with - Fri Apr 05 2019 07:36 PM

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!
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sat Apr 13 2019 11:14 PM

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

Attached picture chassis_mess.jpg
Attached picture spare_parts.jpg
Attached picture chassis_stripped.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Tue Apr 16 2019 08:54 PM

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

Attached picture tuner_unit.jpg
Attached picture dial_face.jpg
Attached picture dial_face_clean.jpg
Attached picture escutcheon_cleaning.jpg
Attached picture escutcheon_done.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Wed Apr 17 2019 12:34 AM

This is quite fascinating to see your work. Have you ever used an ultrasonic bath for this kind of work?
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Wed Apr 17 2019 02:51 PM

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

any recommendations welcome
Posted By: truckernix

Re: Excellent, another radio to play with - Wed Apr 17 2019 05:42 PM

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.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Thu Apr 18 2019 02:55 AM

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.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Thu Apr 18 2019 10:40 PM

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

Attached picture Pwr_Vol_Tone_switch.jpg
Attached picture switch_repair.jpg
Attached picture switch_parts.jpg
Attached picture switch_done.jpg
Posted By: drdoug

Re: Excellent, another radio to play with - Fri Apr 19 2019 01:58 AM

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...
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sat Apr 20 2019 08:54 PM

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 smile

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

Attached picture switch_clean.jpg
Attached picture coils.jpg
Attached picture coils2.jpg
Attached picture coil_broke.jpg
Attached picture coil_fixed.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sat Apr 20 2019 11:49 PM

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

Attached picture dirty.jpg
Attached picture bath.jpg
Attached picture after.jpg
Posted By: drdoug

Re: Excellent, another radio to play with - Sun Apr 21 2019 12:42 AM

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.
Posted By: truckernix

Re: Excellent, another radio to play with - Sun Apr 21 2019 02:33 PM

For folks like me that aren't talented enough to do many of the things that you are doing here, how did you rewind that coil?
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sun Apr 21 2019 04:50 PM

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 smile

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

Attached picture center_coil_loose.jpg
Attached picture coil_apart.jpg
Attached picture coil_wax_only.jpg
Attached picture Oscilator_circuit.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Fri Apr 26 2019 07:50 PM

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.


Attached picture clutch_rubber.jpg
Attached picture clutch_glue.jpg
Attached picture clutch_trimmed.jpg
Attached picture knob_memory.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Fri Apr 26 2019 09:41 PM

If you are OK with the idea, maybe we could get your posts eventually stored as a Tech special.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sat Apr 27 2019 12:00 AM

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.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Wed May 01 2019 05:02 PM

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

Attached picture hot_dip.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Tue Jun 18 2019 12:39 AM

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 smile
it will be our secret for now

Attached picture housing1.jpg
Attached picture housing2.jpg
Attached picture housing3.jpg
Attached picture housing4.jpg
Attached picture housing5.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Tue Aug 06 2019 09:26 PM

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

Attached picture tuner.jpg
Attached picture good_button_springs.jpg
Attached picture weak_button_spring.jpg
Attached picture installing_buttons.jpg
Attached picture all_buttons.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Tue Aug 06 2019 09:27 PM

more photos of tuner unit assembly

- 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.

Attached picture coils_in.jpg
Attached picture antenna_braid.jpg
Attached picture old_wires.jpg
Attached picture soldering_time.jpg
Attached picture complete_tuner.jpg
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Fri Aug 09 2019 09:56 PM

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.

Attached picture mask_for_black.jpg
Attached picture dial_top_white.jpg
Attached picture black_complete.jpg
Attached picture mask_for_tan.jpg
Attached picture dial_black_tan_complete.jpg
Posted By: truckernix

Re: Excellent, another radio to play with - Sat Aug 10 2019 11:15 AM


I think you must have been a watch maker at one time ! This is fascinating to see, very beautiful work.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Sat Aug 10 2019 07:45 PM

thanks for the compliment!
however i don't think i could handle working on watches, i feel i would destroy any watch movement i touch.
Posted By: 2ManyTrucks

Re: Excellent, another radio to play with - Tue Aug 13 2019 04:04 PM

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.

Attached picture dail_maroon1.jpg
Attached picture rear_1.jpg
Attached picture rear_2.jpg
Attached picture front_1.jpg
Attached picture front_2.jpg
Posted By: drdoug

Re: Excellent, another radio to play with - Tue Aug 13 2019 05:32 PM

Following your progress closely... it's looking great!

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