AM Transmitter/Phono Oscillator
Since I haven't done any research on Phono Oscillators, I can only assume that they were simply
used to connect phonograph players to radios. For those not wanting to modify their radios
for a direct phono input connection, this was the easy way to go.
The oscillator on this page is based on the 1939 Zenith S-7000 series, but a few additions and
changes have been made to the original "transmitter" circuit. (Both schematics are
attached.)
In the late 50's and early 60's, many young boys used a similar version of this wireless
broadcaster to play DJ, and broadcast music to nearby homes. I was no different.
The one I used was sold in
kit form by Allied Radio/Knight Kit. (Lafayette also sold one that was a very similar
design.) The "radio station" was professional (?) with dual turntables and a real
microphone. I can still remember pulling the weather report from the daily newspaper, and
running upstairs to check the latest temperature.
This radio is simple to build, and works as expected for its intended design. It won't blast
a signal around the house, but it will give good audio on nearby receivers. Since this is a
simple oscillator, it does transmit harmonics, so don't use this stock version connected to any
outside antenna. Limit your antenna wire to about 9 feet, and keep it close to the target
receiver.
I've seen three versions of the Zenith phono oscillator. Two were mounted on a wood chassis
(including mine), and one was mounted on a metal chassis. Mine was actually a shipping
container for candles. It seemed a shame to dump it in the trash when I could put it to good
use. What you don't see in the picture are three strips of wood added to the top of the
box. This gives the top some added strength and a nice inlaid look.
One word of caution. Always be aware that lethal voltages are present on tube gear.
Always unplug the radio and check for stored voltage from the power supply capacitors before
attempting to service the transmitter.
