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Re: [Amps] Looking for Alpha 87A expertise

Subject: Re: [Amps] Looking for Alpha 87A expertise
From: Douglas L via Amps <>
Reply-to: Douglas L <>
Date: Sun, 14 Mar 2021 20:59:09 -0400
List-post: <>
I have doubts about replacing those PIN diodes with 1N4007’s. The 1N4007’s 
don’t switch quickly enough to substitute for a PIN.


> On Mar 14, 2021, at 3:16 PM, Steve Thompson <> wrote:
>> 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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