Home AM Transmitter (again!)

[Winky Dink]

The saga continues. I picked this up again after two years on the shelf.



Going back to Phil's original schematic and instructions, I still couldn't make it work. Then I tried to build an Antique Electronic Supply kit that I bought some years ago, but I busted the graphite slug in the oscillator coil. I bought a new coil and I busted that one, too.

So I started to build a "Li'l 7" again from scratch. This time I put it on a big board so I could lay it out just like the schematic with all new components.



When it was finished I powered it up, turned on a couple of radios, and adjusted the RF coil until I busted that one, too.



I'm down to my last RF coil, and I'm convinced I'm missing something very obvious, so I'm going to ask you radio-smart people to check what I'm doing one step at a time. Here's step one: Putting in the Audio Signal. I have a stereo phono plug in a CD player. The lines from the left and right channels (tip and ring) are joined to carry the audio in, and the line from the sleeve goes to ground. This is how I have it set up with a 100K pot, and I've followed the signal with headphones all the way to the ll7L7.



So, does this look right so far?

The potentiometer shows a linear 0-100 K ohms until I plug in the stereo plug. After the stereo plug is in, I can't figure out what the potentiometer is doing--sometimes it looks like a bell curve peaking at 25K. And with the headphones, the audio cuts out within 10 percent of the range of sweep.