[AMRadio] Ultrasonic feedback

Peter A Markavage manualman at juno.com
Tue Feb 3 12:54:38 EST 2009

The front panel "gain" control is for the speech clipping gain. If you
turn it up too high, depending on the setting of the "real" audio gain
control which is located behind the key jack, the modulator will squeal.
This is barring any other electrical or component issues.

Pete, wa2cwa

> --- 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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