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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
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
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