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Re: [Amps] Looking for Alpha 87A expertise

Subject: Re: [Amps] Looking for Alpha 87A expertise
From: Steve Thompson <>
Date: Sun, 14 Mar 2021 19:16:19 +0000
List-post: <>
2.  Is a drop from 900V open-circuit to 730V typical when
disconnecting/reconnecting the "R" bias lead at the HV board?  I'm wondering
if I have another leaky PIN diode or cap to ground that is loading it down.
It doesn't take much to load the bias supply given that it inherently has
880k of series resistance.

I don't know the 87A circuits, but assuming the 900V/880k supply is loaded with a reverse biassed diode with 3.9M across it, the current in the 3.9M will drop the voltage to a calculated 734V - close enough to what you're seeing so I'd guess it's ok.

I'd hazard a guess that the 3.9M resistor(s) are there to try and avoid problems from static build up.

Sorry, can't help with anything else.

Steve G8GSQ
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