[Boatanchors] Oscillation in Hammarlund HQ 170A

[Gary Schafer]

I don't know if you got an answer or not John? I would first try bypassing
the power supply leads (B+) to the audio section with larger electrolytic
caps. Any power lead that is dropped by resistors and has a filter cap on it
would be suspect. If that does nothing then look at bypassing the power
leads that go to the IF stages.
Your feedback could be coming back on the B+ lines to other stages.

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of John King
> Sent: Monday, August 06, 2012 6:13 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] Oscillation in Hammarlund 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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