To compute the value of the bottom resistor in the divider string,
don't you need to compute the parallel resistance of the bottom
resistor and the resistance in series with the 1mA panel meter?
Presumably, the internal resistance of the meter is low enough to
ignore.
73,
Jim w8zr
Sent from my iPhone
> On Jan 12, 2017, at 2:09 PM, Paul Christensen <w9ac@arrl.net> wrote:
>
> I've recently acquired an air-cooled version of the Alpha Seventy amplifier.
> I notice that HV reads about 500V low when comparing it to a Fluke DMM with
> Fluke HV probe. The supply is the same as my vapor-cooled version. The
> vapor amp's HV meter tracks in line with the Fluke.
>
> My first thought was that the meter was out of calibration. It's a common 1
> mA DC movement. A NOS replacement meter also reads low by 500V. That
> leaves the five 1-meg HV metering divider resistors but they all measure
> within 1% tolerance as they should -- metal film resistors rarely drift out
> of spec.
>
> So, my plan is to change the value of only the 1-meg resistor on the cold
> end of the 5 megohm string. By computation, I get 500K instead of 1-meg for
> a total string value of 4.5-meg instead of 5.0-meg. Seem like a reasonable
> approach to y'all?
>
> Paul, W9AC
>
>
>
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