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Serviceman's Log

There's an old saying that "one man's trash is another man's treasure". Personally, I think it's all treasure so you can imagine my overwhelming joy when a friend recently found an old valve car radio for me to fix!

Items Covered This Months

  • Astor RM Air Chief Car Radio

  • Celestial ChangHong LT3200HD LCD

  • Grundig Elegance 82 MW82-2101 TV set (NIC/Dolby CUC2058 chassis)

A friend of mine was rummaging around inside his deceased grandfather’s old shed when he came across a couple of old car radios. They weren’t easy to physically locate as they were on the bottom of what used to be a set of shelves which had now collapsed on top of them. Besides that, there was a lot of "junk" in front of them as well.

Note that I use the term "junk" loosely here, as this stuff was really treasure. There’s no such thing as junk in my book.

Click for larger image
The wax paper capacitors inside the old Air Chief AM car radio were all replaced with Philips axial polyester types. Apart from the capacitors, the only other problem was a faulty vibrator assembly.

When he got the first one out into the open, he recognised it as the radio his grandfather had had in his old 1955 Chevrolet. Unfortunately, the old Chevy had also gone to God many years ago.

The car radio was a 1954 Astor (National Automatic Service Co) RM Air Chief. This was a 12V 6-valve plus vibrator AM manual car radio made in Melbourne. Anxious to find out whether it still worked, my friend connected it to a battery and switched it on. The on/off switch needed a little coaxing but eventually the dial-lamp came on.

But that was all. The set was otherwise completely dead and that was when he brought it to me. I gave the vibrator a bit of a knock and although it tried hard, the 44-year old Ferrocart PM238 non-synchronous vibrator just couldn’t quite make it.

In the end, there was nothing for it but to (literally) cut open the metal can to get to the vibrator points and clean them up with a bit of fine wet and dry paper. Thankfully, the points were not too pitted and the reed relay wasn’t open circuit. The spacing was set for "8 thou" (.008 inches or about 0.2mm) and the vibrator then put back in the radio.

When power was applied, you could now hear the vibrator working but there was still no sound from the radio. I reached for my multimeter, intending to connect it to the cathode output (pin 7) of the 6X4 rectifier (to check the HT), but by now smoke had begun pouring from the PT182 transformer.

At first I thought there was a short circuit on the +245V HT rail, probably due to one of the electrolytics. However, the ohmmeter said otherwise. The problem was elsewhere.

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