[Hammarlund] Oscillation in HQ 170A

[Mike Lopez]

I had a similar situation with an HQ 110. After much frustration, it turned
out to be one section of the main filter, believe it or not. The problem was
unrelated to the rest of the audio circuit. I replaced all filter caps, so I
don't remember if it was a lower value section used at the cathode (Bias) of
the audio out tube or one of the other sections. I don't recall if the
multisection can had that lower value in it or not. I no longer have the
radio and the manual went with it. The squeal you describe is exactly my
experience! Your results may differ!
Mike N8AZC


-----Original Message-----
From: hammarlund-bounces at mailman.qth.net
[mailto:hammarlund-bounces at mailman.qth.net] On Behalf Of John King
Sent: Monday, August 06, 2012 6:11 PM
To: Hammarlund at mailman.qth.net
Subject: [Hammarlund] Oscillation in HQ 170A

I pulled an HQ 170A off the shelf to pair up with my HX 500 and found that
the HQ 170A develops an oscillation of about 750 cps when the audio gain is
turned up past half scale. The tone is a guess as to frequency. The controls
and switches are in the range of normal operation.

I had an HQ 180AX that did the same thing and I never found the cause. The
oscillation was not as bad with the HQ 180AX.

Have any of you experienced such an oscillation in a Hammarlund receiver of
this series?

Your input and suggestions will be greatly appreciated. I have cleaned the
tube sockets but have not taken it out of the cabinet to clean the switches.

thanks for taking a look and thinking it over. 73, John, K5PGW
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