[Test-Equipment] HP 403B pegging meters

[Gary Schafer]

Every AC voltmeter that I have seen does the same thing. All the HP's,
balentine etc.

73
Gary  K4FMX

> -----Original Message-----
> From: test-equipment-bounces at mailman.qth.net [mailto:test-equipment-
> bounces at mailman.qth.net] On Behalf Of Howard
> Sent: Thursday, March 13, 2008 2:12 PM
> To: ka4inm at tampabay.rr.com; Discussion of Electronic Test Equipment
> Subject: Re: [Test-Equipment] HP 403B pegging meters
> 
> Maybe a Thermistor inline with that cap or meter lead??
> ----- Original Message -----
> From: "Ron Youvan" <ka4inm at tampabay.rr.com>
> To: "Discussion of Electronic Test Equipment"
> <test-equipment at mailman.qth.net>
> Sent: Thursday, March 13, 2008 9:06 AM
> Subject: Re: [Test-Equipment] HP 403B pegging meters
> 
> 
> > >  Here's my best guess as to what's happening.  There's a big
> > > 1200 microfarad de-coupling cap in the DC negative feedback loop.
> >  >  This is probably necessary in order to get the frequency response
> >  > down to 5 Hz. Until it charges up (through an 8.2K resistor ) and
> >  > the loop can correct itself, theres an > initial rush of current
> >  > through the meter movement. I still can't account for the second
> >  > 'peg', though.
> >
> > >  It would be interesting to know if anybody has devised a way to
> >  > prevent the pegging. Perhaps using some component or trick that
> >  > wasn't available back when the instrument was designed?
> >
> >    Disabling the "meter amplifier" (or shorting out the meter)
> > until a slower capacitor is charged is trivial, but that option
> > was available to the original designer.
> > --
> >     Ron  KA4INM - Please pay your taxes promptly our
> >                   illegal aliens need the free benefits!
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