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Re: [Amps] Looking for Alpha 87A expertise

Subject: Re: [Amps] Looking for Alpha 87A expertise
From: Jim <>
Date: Sun, 14 Mar 2021 21:16:15 -0500
List-post: <>

How fast is a PIN diode?  How fast is a 1N4007 in an Alpha 87? If you have not measured their speed, how can you make that statement?

Jim W7RY

On 3/14/2021 7:59 PM, Douglas L via Amps wrote:
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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