It appears to be a diode ring mixer to me. The diagram is poorly laid out. I'd have to redraw it to make it more sensible to me.
It's designed to take an audio input signal "Input" and an input carrier signal and then mix them. When you "mix" them this way, you should get sum and difference frequencies out (unless the difference is too low).
If you put 3000 hz into input and 5000 hz into carrier, you should get the following frequencies appearing in the output:
- 3000 (original)
- 5000 (original)
- 2000 Hz (5000-3000Hz)
- 8000 Hz (5000+3000Hz)
If instead of a single frequency, you supply "audio" into the input, you can shift the entire audio band up and down by application of the carrier. You normally filter out the upper or lower sideband of interest.
This appears to be part of an audio ring modulator (the output transformer pretty much rules out RF use, depending upon the transformer). But to make it useful as an audio ring modulator, you need to add a filter to isolate the product that you're interested in (normally the sum or difference sideband).
Thanks, I was pretty sure i'd laid it out as plain as possible, but yeah, I'd be happy to see your "redraw". Connecting each of the transformers to opposite sides of the circuit means lots of unconnected pathways crossing eachother on the map. I couldn't think of any less confusing way to lay it out.
So yeah, it is a basic diode ring mod, to which I've injected a basic "bazz fuss" circuit in place of each of the 4 diodes. Having now actually built the circuit, I find that it doesn't seem to do much other than mix 2 audio signals and amplify them a bit. My ears may not be the best, but i could hear no evidence of any sum/difference freqs; perhaps if I could filter as you mention. Any suggestions as to how i would do that?
For the time being I've pretty much abandoned this project in favour of an entirely different circuit which has given me much more interesting results.