[AMRadio] Ultrasonic feedback


John King k5pgw at yahoo.com
Tue Feb 3 14:11:56 EST 2009


There is NO Clipper circuit in this Apache. The clipper tube was removed and the tube socket is empty. This seems to be what many did as a modification. I did have the redrawn schematic showing the mod but have misplaced it. Thanks for the assistance. 73, john, k5PGW 


--- On Tue, 2/3/09, Peter A Markavage <manualman at juno.com> wrote:

> From: Peter A Markavage <manualman at juno.com>
> Subject: Re: [AMRadio] Ultrasonic feedback
> To: amradio at mailman.qth.net
> Date: Tuesday, February 3, 2009, 8:54 AM
> 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
> http://www.manualman.com
> 
> > 
> > --- 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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