[AMRadio] Ultrasonic feedback

sbjohnston at aol.com sbjohnston at aol.com
Tue Feb 3 00:08:52 EST 2009

My Ranger used to do a very similar thing, and the fix in that case was 
to loosen and then retighten all the chassis ground lugs, terminal 
strip mounts, and the like.  Over time the grounds get loose or 
slightly corroded and signals leak around where they shouldn't.

Steve WD8DAS

sbjohnston at aol.com
Radio is your best entertainment value.

-----Original Message-----
From: John King <k5pgw at yahoo.com>
To: AMradio at mailman.qth.net
Sent: Mon, 2 Feb 2009 8:56 pm
Subject: [AMRadio] Ultrasonic feedback

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

My Apache modulator squeals when the microphone gain is raised and the 
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 
section. I am going to go through the section with a screwdriver and a 
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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