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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