[Test-Equipment] Re: Test-Equipment Digest, Vol 46, Issue 4

[Jeff Furman]

Ken, I've retrofitted a 403b with AA cells. I worried about getting the 
voltages just right, but, I tried the simple way first. The circuit has 
some large value electrolytics that need to charge up at turnon, 
especially in the extended low frequency response mode (I think that's 
1Hz.) HP says that the meter needs some seconds to stabilize. I can 
guess that these capacitors need to reform for a while to 
reduce their leakage currents, as well. My meter also has that frustrating 
offset from zero, I think a small division or less-- is that from noise, 
leakage, or oscillation, I don't know.
Jeff AD6MX

  > > Message: 2
> Date: Wed, 6 Feb 2008 22:08:54 -0500
> From: "Ken & Marlene Grant" <the_grants at sympatico.ca>
> Subject: [Test-Equipment] HP 403B AF voltmeter
> I've just bought one of these units. It didn't come with the battery pack, so I made up an array of zeners, fed from the built-in battery charger, as a substitute. Is this a legitimate way to power the instrument or was it really meant to be battery powered? How critical are the supply voltages?
> Also, on power-up, the meter movement goes full scale momentarily before trying to settle down to zero ( which it doesn't manage to do, on the lower scales ). Is this normal? The manual doesn't mention such behaviour.
> I have it opened up on my bench. Could it be picking up external 'hum', accounting for the inability to zero?
> I'd really appreciate any help or advice from the group. Ken, VE3FIT