[Hammarlund] HQ-170 Audio

[Charles Ochs]

In following this thread, this is the best advice that I have seen here, in terms of a good troubleshooting method. This may very well turn out to be one of those nasty little IF cans that were used in the HQ-110, and other receivers of similar vintage. These, as anyone who has been down this road before will testify-are a royal PITA. When I encounter one of these in a set that needs its internal capacitors replaced, the bill goes up by $50.
Chuck N1LNH
 
> Date: Mon, 21 Feb 2011 09:51:29 -0500
> From: k2cby at optonline.net
> To: hammarlund at mailman.qth.net
> Subject: [Hammarlund] HQ-170 Audio
> 
> Ray’s note that turning down the audio gain control reduced but did not kill
> the noise
> suggests to me that the source is something riding on the B+ buss.
> 
> With the audio gain up, the noise would be amplified by the detector and 1st
> audio stages 
> and passed through to the output stage as a large signal.
> 
> With the audio gain fully down, the noise would be greatly reduced but it
> would still be 
> present on the plate and screen of the output stage only and would not
> totally disappear.
> 
> In locating hum & noise troubles, I have had good success hanging a very
> large value mylar 
> (.1 µF) or small value (2 µF) electrolytic with appropriate voltage ratings
> from grid to ground, 
> plate to ground, and B+ to ground at each of the various stages. When the
> noise vanishes, 
> you have found the stage to troubleshoot. Just be sure to discharge the
> capacitor each time 
> before reconnecting it. 
> 
> 
> 
> Miles B. Anderson, K2CBY
> 16 Round Pond Lane
> Sag Harbor, NY 11963
> Tel.: (631) 725-4400
> 
> Fax.: (631) 725-2223
> e-mail: k2cby at optonline.net 
> 
> 
> 
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