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 air.

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!