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

[Eli Shvarzman]

Try to replace the pots. With 10 turns halipot.


-----Original Message-----
From: Test-Equipment [mailto:test-equipment-bounces at mailman.qth.net] On
Behalf Of Barry
Sent: Thursday, September 04, 2014 5:58 PM
To: Discussion of Electronic Test Equipment
Subject: [Test-Equipment] Using an HP 331A Distortion Meter

Another question about the 331A.  Does anyone have experience
cleaning/replacing the balance pots?  Mine are very touchy.  They appear to
be the sealed type and I realize I can most likely pop the back off the
piggy-backed one, but not sure about the "front" one and I'm wondering if
I'm opening a can-of-worms with this.

Anyone tried this with these particular pots?  Anyone know if there are NOS
parts to be had for them?

Other than perhaps some switches that could use a little DeoXit, this little
unit appears to work quite nicely.

Oh, and, anyone know where a full schematic can be had for this model
online?  The manuals I've found only have parts and pieces of the schematics
and I have yet to find a full schematic.

Thanks again,
Barry - N4BUQ

----- Original Message -----
> From: "Barry" <n4buq at knology.net>
> To: "Test Equipment" <test-equipment at mailman.qth.net>
> Sent: Tuesday, September 2, 2014 3:58:32 PM
> Subject: Re: [Test-Equipment] Using an HP 331A Distortion Meter
> 
> Thanks for the replies.  I thought the meter/analyzer has a high-impedance
> input so terminating the input into whatever impedance it needs to see is
> the primary consideration.
> 
> I was thinking of this more in the RF sense where the output of the
generator
> needs to be terminated properly AND needs to match the input circuit (e.g.
> antenna, etc.) but that's not the case here with the high-impedance input.
> 
> Thanks again,
> Barry - N4BUQ
> 
> ----- Original Message -----
> > From: "David DiGiacomo" <david at davmar.org>
> > To: "Barry" <n4buq at knology.net>
> > Cc: "Test Equipment" <test-equipment at mailman.qth.net>
> > Sent: Tuesday, September 2, 2014 3:13:40 PM
> > Subject: Re: [Test-Equipment] Using an HP 331A Distortion Meter
> > 
> > On Tue, Sep 2, 2014 at 2:07 PM, Barry <n4buq at knology.net> wrote:
> > > I'm a bit new to using a distortion meter and have a basic question.
> > > When
> > > connecting the device I want to test to the meter's input, I assume it
is
> > > necessary to terminate the generator properly (e.g. into a 600-ohm
> > > resistor, etc.) and that's so that the generator sees the proper load.
> > >
> > > What's confusing me a bit about this I may use this to measure
distortion
> > > for a 600-ohm-terminated signal as well as connecting it to the 8-ohm
> > > load
> > > for the PA output.
> > >
> > > Does the meter not really care what impedance it sees on the input?
It
> > > just seems odd that I would feed it a 600-ohm load in one case and an
> > > 8-ohm load in another.
> > 
> > 
> > The distortion analyzer has a high impedance input, so it doesn't care
> > what the source impedance is, as long as it's not too high.
> > 
> > However, the distortion of the source will vary depending on how it is
> > loaded, so you should connect the load that is relevant to your
> > application (or if you are testing against a specification, the load
> > that is specified as a test condition).
> > 
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