[Hammarlund] HQ-170 audio

[RAY FRIESS]

Les ..   The 170A uses an OA2 voltage regulator.
 
One reason I thought the audio or driver is that even with the volume control all the way down, I can still hear the static crashes, just not as loud.
It would seem to me that if the noise was generated prior to the audio section, with the volume control down, it would go away entirely.
The fact that it remains with the volume all the way down, would seem to indicate that it is being generated either in the audio driver, or the audio output
because it is still audible.  With the volume control down there should either be nothing driving the audio output tube, or if it were in the driver tube the
noise being generated in the driver was being supplied to the audio output tube.
 
I must admit that I have never seen a voltage regulator tube cause static crashes, so I find that interesting Les.
 
In my experience, I have found tubes exhibiting microphonic noise response.  Usually a tube presents that problem due to the elements wiggling or aging
and becoming susceptible to vibrations such as occur with the tapping of a front panel, chassis or cabinet.  The vibrations are transmitted into the tube,
causing the microphonic sounding noise, which sounds different from the "static crashing" type of noise one hears from a bad tube.
 
I have used the "tube tapping test" over the years too.  I havent tried it yet because I will have to pull the receiver out of its position on the operating bench.
 
My thoughts on making the inquiry about anyone having spare ones to part with was to get ready in case it comes down to that being the cause.
 
Ray
 


From: leslocklear at cableone.net
To: 1oldlens1 at ix.netcom.com; rayfrijr at msn.com; hammarlund at mailman.qth.net
Subject: Re: [Hammarlund] HQ-170 audio
Date: Sun, 20 Feb 2011 18:40:14 -0600





I have seen voltage regulator tubes make static crashing noises on several different receivers, including a R-390A and SP-600. I don't have a book handy, does the 170A use an OA2 like the 180A? Swap regulator tubes just to eliminate that as a source. Or, tap on the tube with a wooden lead pencil eraser.
 
Les Locklear
Gulfport, Ms.
DX'ing Since '57
 
 
 
 
 
 
 
 

----- Original Message ----- 
From: Richard Knoppow 
To: RAY FRIESS ; hammarlund at mailman.qth.net 
Sent: Sunday, February 20, 2011 6:30 PM
Subject: Re: [Hammarlund] HQ-170 audio


----- Original Message ----- 
From: "RAY FRIESS" <rayfrijr at msn.com>
To: <1oldlens1 at ix.netcom.com>; <hammarlund at mailman.qth.net>; 
<boatanchors at puck.nether.net>
Sent: Sunday, February 20, 2011 3:35 PM
Subject: RE: [Hammarlund] HQ-170 audio



The microphonics are still present even with the volume 
control all the way down.
The noise (static like crashes) decrease with the volume 
control all the way, down but are still present, just barely 
though.
By microphonics, I mean that when I tap the cabinet or front 
panel, you can hear the coming through the audio section.
Before the noise started in the audio section, it was not 
present.

I have had the receiver gone completely through by an expert 
in Hammarlund receivers.  When he sent it back after going 
through it,
he said it was as close to factor specs as he had ever been 
able to get a receiver of its age to.

Ray

     There may be two different problems. If the "static" 
goes away with the volume control down its generated ahead 
of the audio stage. You may be able to isolate it by pulling 
tubes to see what makes the noise go away.
     The microphonics may be from a bad tube but I again 
suggest tapping and poking at things to see if you can 
isolate it. Without another tube to substitute its difficult 
to isolate it to the tube but even if another tube works 
better it may be that the socket or tube pins are oxidized 
which can also cause a similar microphonic problem. Cleaning 
the pins with a toothbrush or even a Brillo pad and cleaning 
the tube socket with some Deoxit and then working the tube 
in it may help.
     Don't count on your "expert", there may still be 
problems.
     Neither of the audio tubes is rare or expensive and a 
web search should find some at reasonable prices.
     Unfortunately, few tube testers have any means for 
testing for microphonics. I will say that its normal for 
tubes to have just a little but not what you describe.



--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com 

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