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Re: [Amps] HV Diodes

To: Manfred Mornhinweg <>, "" <>
Subject: Re: [Amps] HV Diodes
From: Steven Katz <>
Date: Thu, 16 Oct 2014 22:42:38 +0000
List-post: <">>
Actually, the SCH5000s found their way into the old ETO/Alpha amps when Ehrhorn 
was in Florida and we had a good Semtech sales engineer there.  Dick had 
previous experience working for NASA and ECI and other places using hi-rel 
parts and was comfortable with them.

Semtech HV rectifier assemblies were also widely used in Henry amps, right 
after they got rid of 3B28s and stuff.  That's because we had a good Semtech 
sales engineer there also, who was Mel WB6FDR (now W6FDR).  Same assemblies 
were also widely used in Harris/RF high power transmitters and amplifiers, 
because we had a good Semtech sales engineer there as well, WB2WIK.  :)

But they were "mostly" used in defense/aerospace programs where the same design 
assemblies would be 100% X-rayed, serialized, and burned in for 168 hours at 
high temperature reverse bias (usually 10% above rated PRV and at 100 degrees 
C), with "life test" samples running in parallel at full power for 1000 hours 
and data collected.  If anything failed during these tests, the whole batch 
would be rejected or subject to 100% re-screening.

Since they were designed to withstand all that, the "commercial" versions are 
pretty good, as they used the same parts and the same designs.

Circular dice reduce voltage gradient stresses at the edges of the die (no 
corners for them to build up).  Yes, it wastes some silicon.  They're not 
"sawed" they're ultrasonically cut and have very smooth edges with no corners - 
another thing that added to reliability under reverse stress condx.




your account of the SCH-5000 is really interesting! So these were very high 
quality diodes for special high-rel applications. Using circular dies must be a 
pretty rare thing, I guess, because of the additinal etching and the lower 
amount of parts per wafer.

How did those high cost parts find their way into ham equipment? I mean, a 
power rectifier in an amp's power supply really doesn't need to have such ultra 
low reverse current specs! As long as the better diodes in a string can handle 
the leakage of the worst ones in avalanche mode, without failing, that should 
be good enough!

Could it be that at some point these quality diode modules became available as 
surplus at low cost, and then the amplifier manufacturer grabbed them?

Just guessing again. Darn. Carl told me to stop guessing! ;-)



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