[AMRadio] Ultrasonic feedback

John King k5pgw at yahoo.com
Mon Feb 2 21:56:47 EST 2009

Can anyone direct me to a source of information or a tutorial on Ultrasonic feedback in modulator circuits such as that in the Heathkit Apache.

My Apache modulator squeals when the microphone gain is raised and the modulator tubes draw a lot of current. As long as the microphone gain is kept very LOW the current does not take off and there is no squeal coming from the modulator section. I am going to go through the section with a screwdriver and a nut driver to tighten up the grounds to the chassis and tube socket.

Ultrasonic feedback is a NEW phenomenon to me. Someone mentioned ferrite beads some time back. Thanks for reading. 73, John, K5PGW


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