[AMRadio] Ultrasonic feedback

KC8OPP Roger S. kc8opp at yahoo.com
Tue Feb 3 07:32:38 EST 2009


Not sure about the Apache, but I do have a Viking II here and the manual tells you to reverse the modulator plate connections if you hear a squeal from the modulation circuit.

Sorry if I am off topic too far.


--- On Mon, 2/2/09, John King <k5pgw at yahoo.com> wrote:

> From: John King <k5pgw at yahoo.com>
> Subject: [AMRadio] Ultrasonic feedback
> To: AMradio at mailman.qth.net
> Date: Monday, February 2, 2009, 9:56 PM
> 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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