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Re: [Amps] Looking for Alpha 87A expertise (David W6DR)

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Subject: Re: [Amps] Looking for Alpha 87A expertise (David W6DR)
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Date: Mon, 15 Mar 2021 09:57:36 -0700
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I wouldn't say I am an expert on the Alpha 87A although I did own one and
deal with issues inside it for several years.  It was a good amp and its
best feature was the quiet and reliable PIN diodes making real QSK not only
possible, but normal.  I never managed to kill mine.  I did trade it in to
Alpha for a 9500.  As far as PIN diodes are concerned, you can download the
SPEC sheet from Micro-Semi (UM4006D/SM) and for 1N4007s you can download the
Spec sheet from any company that makes them.  UM4006D/SM PIN diodes run
about $16 per; 1N4007 diodes run about $0.03 per.  So on price it ought to
be fairly obvious that there is a difference here.  Looking at the spec
sheet, the speed of switching of the UM4006D is incredibly high (like 5
uSec) - the 1N4007 doesn't appear to be specified except to confirm that it
works well at 60 Hz.  If 60Hz works for you - go for it.  But this is a T/R
relay we are talking about and you don't want the power going to the wrong
place for very long.  And 1/60 second is VERY long for 1500 Watts to be
going to the wrong place. (1/60 second = 16700 uSec).
>From what I have read, the failures tended to occur in earlier units due to
a less than optimal installation protocol during manufacturing. (10/05/2017
Amps Post from WC1M).
Microchip Technology Inc. appears to have units available for sale right now
- possibly others, and there appear to be alternates available.
I am enough of an expert to know that I would rather replace a dead part
with a same thing replacement than attempt to reengineer a critical circuit
that will kill my expensive transceiver in a few microseconds if I get it
wrong.  Especially if the part costs less than $20.  Good luck.
Dave W6DR
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