[ARC5] Meter Calibration and HV probe

[Fuqua, Bill L]

the 1 MOhm in probe prevented loading of RF circuits when probing DC voltages on such things as grids and plates.
If it was not there the stray capacitance of the probe lead would detune the circuits.
73
Bill wa4lav

________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] on behalf of Kenneth G. Gordon [kgordon2006 at frontier.com]
Sent: Saturday, August 03, 2013 5:58 PM
To: ARC-5 List
Subject: Re: [ARC5] Meter Calibration and HV probe

On 3 Aug 2013 at 16:38, D C _Mac_ Macdonald wrote:

> Somewhere in the recesses of my memory I seem to remember that the 11
> Megohm rating of so many VTVMs "back in the day" consisted of 10 Meg
> in the instrument and another 1 Meg resistor in the probe!

You're absolutely correct, Mac. I have two Heathkit VTVMs here, which I use regularly, and
both are set up the same way: 10 meg in the instrument and 1 meg in the probe.

Someone some time ago published on the web a modification to include the 1 meg inside the
instrument instead of in the probe. However, that turned out to not be such a hot idea after
all.

Also, I have two Heathkit HV probes here (up to 30 KV) and a Simpson version. I have used
those with a couple of different versions of DMMs and the voltage readout was always very
close to the readout when connected to a Simpson 260. In fact, it was close enough that I
never bothered about "calibrating" it any closer. The difference between 10KV and 10.1 KV
isn't enough to worry about at that level.

Ken W7EKB
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