AM Radio Transmitter
You're right, this is not an antique. Despite its
vaguely old-fashioned appearance, the manufacturing date is 1996!
I built this small transmitter from a kit available from
Antique Electronic Supply. Modeled
after the 1939 Zenith S-7000 Wireless Record Player, the
transmitter accepts any high-output audio source and
broadcasts an AM signal for your antique sets to receive.
The kit employs a grand total of 18 electronic components,
including the single 12SA7GT tube, and it requires only
elementary soldering skills. I was able to assemble
it in a single evening.
At the left in this photo you can see three Fahnestock clips
for connecting an external antenna, audio input, and
ground. You tune the transmitter by adjusting its tuning coil
(with the supplied tool) to broadcast in any quiet spot on
the dial between 1100 and 1600 kilohertz.
The kit comes with a nice little wooden base,
rectangular in shape. I happened to have an oval
base left over from some other project, and used that
instead. As supplied, the kit doesn't have an on/off
switch. You just plug it in when you want to go on the
If you want to get fancier, it would be simple to
enclose the circuitry in a box (don't forget some
ventilation holes!) and mount a power switch. You could
also mount a jack for the audio input, depending on
what you plan to use for an audio source.
A pretty easy project, and building it can
give you some insight into what it was like to build
all those relics you've got lying around the place.
The sound quality on this transmitter is good, but
the range is not spectacular. The FCC puts severe limits on
the broadcasting power of such unlicensed
"flea power" transmitters. I had to attach a
pretty long antenna wire to get any distance at all.
If you have an old signal generator, such as my
old EICO Model 324, you may
already have what you need to duplicate this unit's performance.
In our Building section, you will find an
article explaining how to build a similar AM broadcast transmitter, the
"Li'l 7." That article includes a complete parts list and explanation of
how the transmitter works. If you prefer to roll your own, check it out!