If your radio has 6 volt tubes in it, it is likely made for 6 volt operation. Unless you have a universal transformer in the radio, to convert the radio to 12 volts, you must replace all the tubes with 12 volt equivilants, and put a ballast resistor of sufficient wattage and ohmage to drop the current going to the vibrator and transformer down to about 6.8-7.2 volts with the generator running at high idle (1,000 rpm). If voltages seem low in the B+ section, perhaps the transformer is designed for 12 volt operation. You can try the transformer on 12 volts without a ballast, but doing so with the wrong transformer can damage the vibrator and transformer.
Basically what I am saying with all of this detailed bla bla is that changing the tubes from 6 volt filaments to 12 volt filaments is not all it takes to convert the radio. Try to look up as much service information on this radio as possible, and read, in detail, all of the various changes and power options the company made available for that radio in 1955. Chevrolet changed over to the 12 volt charging system in the middle of that year, so you can't be sure what you've got. It is entirely possible that the radio is designed for 12 volt operation. In that case you may hook it up to 12 volts without worry.
Thomas
:I am repairing a old radio that I was told came out of a 1955 Corvette, when I took off the cover to get the Modle # it had one sticker taped over another. The top one said it had all 12 volt tubes. The bottom one said it had all 6 volt tubes. Was this a practice that they did years back to convert a 6 to a 12 volt radio? It is a wonder bar radio and has 9 tubes all of them are 12 volts. I wonder which shematic I should order. any Ideas?
Hello Ralph,
The 6 Volt and 12 Volt Corvette radios (1953/54 and 1955) were very similar in appearance, in fact the Delco service literature used the same photo for both. Looking at the service manuals for both radios, they are also quite similar, except for the obvious 12 Volt components.
6 Volt was model 3706551, 12 Volt is model 3711897. Some differences noted in the manuals are:
The 6 Volt power supply section has a choke coil and .5 mfd. capacitor mounted on top of the power transformer (part No. 7239124), and under the power chassis, a 220 ohm resistor across the vibrator points, and a .006 buffer capacitor across the 0Z4 plates.
The 12 Volt power supply has the choke coil and ( 2) .5 mfd.caps mounted under the chassis, nothing mounted on top of the power transformer (part No. 6067). One of those .5 mfd. caps replaces the 220 ohm resistor of the 6 Volt version. Also, the buffer is changed to a .007 mfd. cap in series with a 15k resistor across the 0Z4 plates.
Please note that like other manufacturers, Delco often made running changes that were not documented in their service literature. But, I hope that the above information helps you to determine which radio you have.
Meade
They wouldn't have put the 12 volt label over the 6 volt label, unless the set was a 12 volt set.
Simply changing the tubes, vibrator, and pilot lights to 6 volts or to 12 volts, does not completely change the set. The transformer must receive the proper voltage to operate properly. If it's designed for 12 volts, and you feed it 6 volts, the set will run at half voltage. If it's designed for 6 volts, and you run it at 12 volts, you'll have burned vibrator points, and you'll overheat the transformer.
You must do a lot of thorough reading on radio and electrical theory before you convert the set, if you must convert the set. This is not just a simple task of changing tubes. As was said before, though, your set is probably a 12 volt set. If you use it with a modern 12 volt electrical system, you don't need to make any changes.