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Re: [Amps] PIN Diodes /1N4007 / ALPHA 87A info

To: "'HP'" <>, <>
Subject: Re: [Amps] PIN Diodes /1N4007 / ALPHA 87A info
From: "Jeff DePolo" <>
Date: Wed, 17 Mar 2021 09:59:49 -0400
List-post: <>
I'm the OP on the topic of the 87A troubleshooting.  Just a couple of

> The bottom line is that replacing a PIN diode with a switching diode might
> work depending upon the control voltage and the signal voltage, but it
> completely changes the switching mechanism involved and it would NOT be
> universally applicable.

To be clear, the PIN diodes that I was discussing are in the receive RF
path.  They are reverse-biased to 700+ volts when the amplifier is in
transmit mode with a total of four diodes in series to minimize the
capacitance.  When in receive mode, they are forward-biased in pairs by a
34V supply through 200 ohms, or around 150 mils through each. 
Given your expertise on the subject, could you answer one of my previous
questions regarding why a high-value resistor (3.9M) is shunted across the
diodes?  Does it affect recovery?

                                        --- Jeff WN3A

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