Common Issues with Vintage Truck Radios
You've managed to match the original paint color of your
vintage Chevrolet truck,
you've got the gauges wired correctly, and the seat-covers have been replaced,
but what you really want is tunes. You could replace the existing radio with a
modern set that has retro-styling, or you could keep things authentic and repair
the original. There are four commonly occurring issues with old radios, and most
are not even that expensive.
Volume Potentiometer: These tend to get pretty noisy with age,
largely because of dirt and dust, or wear to the carbon element. Use canned air
to clean the dust away - it will help.
Capacitors: These will either wear out, or leak. There are paper
filter capacitors for audio bypass and power supply that should be replaced,
while the power supply filer capacitors should also be exchanged for new ones.
They fail because the electrolyte dries out, and causes an internal short. A
capacitor short can cause damage to the power transformer, so it's essential
that these be in pristine condition.
Vibrator Buffer Capacitor: This is a timing capacitor and it is
crucial for suppressing voltage spikes that the vibrator generates. This
capacitors is rated at a much higher voltage than any others in the radio.
Bad Vibrator: When the vibrator degrades, it effects the DC. Older mechanical vibrators work just fine, as long as the contacts are good, but they can fail without warning. It may be simpler just to replace the vibrator with a solid state unit, which are both quieter and more reliable. They're not that expensive, either - only running about $30. If you do replace the vibrator you MUST also replace the buffer capacitor (listed above)
Most vintage radios were 6
volt sets, while modern truck radios are generally 12 volts. There are kits to convert 12 volts to 6 (positive or negative) should you
choose to install a modern radio instead of repairing the original.
Also, the number of tubes in a radio changes from model to model. Most have six, but the single unit 5-band from 1941 used nine, and there are a few that had five or seven as well. The Stovebolt Page has a list of radio models by years, with model numbers and the number of tubes for each.