[AMRadio] Ultrasonic feedback

Bob Macklin macklinbob at msn.com
Mon Feb 2 22:01:37 EST 2009

Does it happen with the microphone disconnected?

Bob Macklin
Kent (Seattle), Wa,
"Real Radios Glow in the Dark"

----- Original Message ----- 
From: "John King" <k5pgw at yahoo.com>
To: <AMradio at mailman.qth.net>
Sent: Monday, February 02, 2009 6:56 PM
Subject: [AMRadio] Ultrasonic feedback

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