Tales from real life
I turned 15 in May and my new ‘maturity’ came with a new interest in things like girls and Rock ‘n’ Roll music. My ’53 Studebaker pickup hadn’t come equipped with a radio, of course, so I scrounged one from the junked cars in the old pothole. My search was limited to a narrow range of cars: old enough to have a six-volt electrical system, but new enough to have a radio. I don’t remember which model I found, but it had a radio installed, complete with speaker, as a self-contained unit. It was perfect for my purpose. Most surprising of all, it still worked.
The technology of 1950’s radio required vacuum tubes, and vacuum tubes require 250 volts DC. This could be provided by a simple transformer/rectifier circuit in a 110 volt AC tabletop radio, but how do you step up a six-volt DC battery? The ingenious solution was a mechanical ‘vibrator’ that simulated AC current by breaking the six-volt DC circuit path sixty times a second. It was basically just a relay wired to open its own coil when power was applied. One set of relay contacts would close to send power to the transformer and another set would open to remove power from the relay coil. The relay would rapidly alternate positions as long as power was supplied to the radio. The series of DC current pulses worked just as well as AC power for the transformer/rectifier in the car radio. The buzzing of the vibrator circuit was clearly audible if the radio volume was turned down with the engine off.
The installation challenge was that my pickup didn’t have a dashboard like modern cars. The instruments were installed directly into the firewall with their connecting wires visible under the hood. Since there was no obvious way to mount the radio on the firewall, I used some baling twine and tied it next to me in the middle of the bench seat. I’d also taken the fender mounted antenna when I grabbed the radio unit. A couple of new holes in the pickup cab allowed me to mount the antenna and run the antenna cable behind the seat to the radio. The small hole we’d drilled in the firewall to access the freeze plug turned out to be perfect for running the power wires.
The lash-up must have looked ridiculous, but it worked like a dream. I had my tunes on all summer as I cruised around pretending to be cool. Looking back, I can hardly believe it was even possible. Delicate vacuum tubes and a mechanical vibrator don’t seem well suited for bouncing around in a moving car.