[Hammarlund] HQ-170 Audio

[Carl]

I mentioned replacing Z-2 yesterday which appears to have floated above 
anyones vision.

Now I wonder how many commentors actually have a HQ-170 or have looked at 
the schematic before posting?

That little circuit is known as a Couplate when its a Centralab and other 
companies have their own pet names. To any tech worth his price its known as 
trouble and is automatically replaced. Now Ive seen several 170's using 
discrete components so cant say if Hammarlund changed in production, later 
in their Service Dept or it was done by someone else.

The fix of course is to use discrete components and the values are on the 
schematic.

If the noise is still there then at least one trouble spot has ben 
eliminated.

Carl
KM1H


----- Original Message ----- 
From: "k2cby" <k2cby at optonline.net>
To: <hammarlund at mailman.qth.net>
Sent: Monday, February 21, 2011 9:51 AM
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



______________________________________________________________
Hammarlund mailing list
Home: http://mailman.qth.net/mailman/listinfo/hammarlund
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Hammarlund at mailman.qth.net

List Administrator: Duane Fischer, W8DBF
** For Assistance: dfischer at usol.com **


This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html