[Test-Equipment] Using an HP 331A Distortion Meter

[Barry]

Resurrecting an old thread, I had an opportunity to spend some time on this meter yesterday.  I have a 652A which had a rather noisy amplitude pot.  I was able to disassemble and clean it and it now works great.  Intending to do the same to the balance pot in the 331A, when removed the pot and pried the fingers open, I could not pull the pot apart.  Odd that they are both Clarostat pots that look pretty much identical but, try as I may, I could not get it to budge (perhaps it is sealed whereas the other one was not?).  I was, however, able to remove the "C" retaining clip which release the pressure from the wiper and the carbon disc on the "fine" adjust pot (100 ohm).  With that, I rotated the shaft several times very quickly, hoping to release any lodged carbon dust, etc. from the wiper and then reassembled the clip.

When I tested it, the vernier adjustment seemed quite a bit smoother so maybe that was enough (for now).

I'm quite pleased with this instrument!  I hadn't spent that much time with it but have cleaned it up a lot and have confirmed that it does yield a very smooth null (my HP209 appears to have about 0.8% distortion so that's good!).  Of course, it isn't fully tested or calibrated but at least it does seem to be very functional.  The output terminals also produce the correct output as well.

Anyway, just thought I'd circle back on this and report back on it.

Thanks,
Barry - N4BUQ

----- Original Message -----
> From: "Dale H. Cook" <radiotest at plymouthcolony.net>
> To: test-equipment at mailman.qth.net
> Sent: Saturday, September 6, 2014 6:50:33 AM
> Subject: Re: [Test-Equipment] Using an HP 331A Distortion Meter
> 
> At 06:57 AM 9/6/2014, Eli Shvarzman wrote:
> 
> >Use single hlipot potentiometer, there is hlipots  having the same diameter
> >as the original potentiometer
> 
> He could install a single multiturn Helipot in place of the original dual
> control, but some of us prefer to restore our classic laboratory grade
> instrumentation. It all depends upon his desires and needs.
> 
> Dale H. Cook, GR / HP Collector, Roanoke/Lynchburg, VA
> http://plymouthcolony.net/starcity/radios/index.html
> 
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