A while back now I took on a project for a friend. A 1933/34 Zenith “Glove-box” automotive radio.
This is the first picture I took of it- not a very good one but you can see that it was rusty, missing the knobs and generally full of old dead spiders and dust.
I stripped the radio down. The lower half of the chassis is at a 45-degree angle and houses the speaker and power socket. That was removed so it would sit flat. I pulled the dial bezel and glass aside to safety as the glass was unbroken and in good condition. The dial face was equally in good shape so was removed and stored safely after a gentle cleaning.
I repainted the bucket the dial sits in and finished the face.
I tested all the wound components and they were good. That was good because they’re the hardest parts to source and replace if they are bad.
I cleaned up the screws. In the image, the one on the right looked like the one on the left to begin. The set has some nice panel-headed screws that hold the chassis in the frame that are prominent on the front and sides. So, I spun them against a file and de-burred the surfaces, polished and nickel-plated them.
I started to clean the power supply chassis up. The capacitors were past their prime when the set was in operation and the mess there is a mixture of wax, capacitor dielectric paste and dirt- the set was also home to quite a few spiders, all of which were petrified and crispy. The failure there where the main smoothing capacitor had vented was also likely the reason for the set being removed. that would have caused the fuse to blow every time it was switched on.
The power chassis cleaned up well enough to continue. There are a lot of high voltage parts in this section, all of which tested bad. It also runs quite warm, being encased in a metal box with no ventilation- to prevent RF noise.
The volume control also tested bad. the schematic showed it to be 1 MegOhm from end to end but it had dropped in value (odd behavior, usually they go up) which meant that the set would never be adjustable to quiet, it would start at loud and get louder. I had never seen a potentiometer like this before- a good design in theory. Normally in a carbon track device there is a phenolic wafer with a carbon trace printed on it, and a metal finger that touches the carbon as the center tap. As you dial it round, the finger slides across the carbon. Eventually the track wears out and the potentiometer becomes noisy and unreliable. This one had a carbon track and a spring-steel ribbon that was slightly smaller than the inner track. A finger pressed the ribbon against the track, making the contact and the only friction was of the finger against the spring steel, which would last a very very long time. As the ribbon was only pressed against the carbon and not dragged, it would also last. I think the carbon track, printed on cardboard, had become damp and deteriorated that way. so, I replaced the volume control and power switch with a new one, modified to suit.
I replaced all the old paper and wax capacitors and after more than half of the old resistors tested bad (most had either gone open circuit or had drifted very high resistance) I replaced them all with high stability metal film 1% devices.
I managed to get the old mechanical vibrator apart, clean the contacts and get the high voltage to come up operational. First test was positive, nothing smoked up and I was able to just about get a local radio station to come out of the speaker, proving all stages of the radio were at least operational. The vibrator, which interrupts the input to the power transformer providing a rudimentary AC, was very loud, almost intolerably so. So, I purchased a solid state one which is very efficient and mostly quiet, changed the socket for a new porcelain one (the old one had 6 pins, this one a more standard 4) .
With the electrical portion of the radio working as expected, I set about tidying up the cosmetic parts of the case. The face was rusty, so I took to it with my DA sander and removed the pitting and rust.
I left the smaller dents because they are part of the original character- there were a couple bigger dinks that I knocked out. All down to bare metal, it was time to prime and paint.
The original paint finish was wrinkle-black. I bought some of this horrible finnicky paint and redid the front in it. First revision above, part of it bubbled (it has to be heated) and the rest went psycho-insane and wrinkled up like craters on the Moon. Second revision went much better and has the correct finish.
I then redid the rest of the case (three attempts for the main case, another three for the lid).
I cleaned all the rust off the dial beauty ring, polished it and clear-coated it.
I was able to carefully remove a very fragile remnant of grille cloth from where it was attached to the metal behind the grille aperture. I washed it and the pattern became visible- most of the cloth had rotted and was just threads. I found a company in Shreveport, LA who was re-manufacturing original Zenith grille cloths, so bought a length. A very rich color, in shiny thread as per the original.
The grille cloth, glued to the freshly painted case. Looks most excellent.
I got the Dremel out again, removed the rust from the clip, polished and nickel plated the clips that hold the lid on.
I bought some nice yellow cotton covered cloth to fit and replace the very dry, crispy original wires that led to the tube top caps. This keeps the nice period look but gives new wire. All re-aligned for its’ home in the case, picking up a bunch of local stations during the day.
A couple of new original-style knobs finished the radio off, and an auxiliary-in socket for when the AM radio has nothing to offer.