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Re: [Amps] HV Diodes

To: Paul Christensen <>, Amplifier Mailing List <>
Subject: Re: [Amps] HV Diodes
From: Steven Katz <>
Date: Thu, 16 Oct 2014 20:41:49 +0000
List-post: <">>
The SCH-5000 is unique and not very similar to other "similar looking" HV 
modules.  It uses fused metal-oxide encapsulated (hermetically sealed) 
rectifiers having a .060" circular die metallurgically  bonded to solid silver 
leads, and the leads are welded with the corners rounded (to prevent corona 
inception) prior to vacuum potting with a very good thermally conductive epoxy, 
Emerson-Cuming 2650FT.  All the diodes are closely matched for breakdown 
voltage prior to assembly and welding, and the finished assemblies are X-rayed. 
 The diodes themselves have very low leakage, way below specification (normal 
spec was 1 uA at 5000V, but diodes were tested to be about one-tenth that) and 
they're all high temp avalanche devices that can handle a lot of avalanche 
energy if needed.

Ratings aren't particularly high, but "burned in" versions of exactly these 
same assemblies are used in missile systems, jet engine exciters, and many 
defense/aerospace applications all over the world since the 1970s.  I wouldn't 
compare them with much "off the shelf" stuff.


-----Original Message-----
From: Amps [] On Behalf Of Paul Christensen
Sent: Thursday, October 16, 2014 1:15 PM
To: Amplifier Mailing List
Subject: Re: [Amps] HV Diodes


Regarding Alpha, the 77Sx (dual 8877) uses a quad set of Semtech SCH5000 
modules rated at only 5KV/0.5A.  The current rating is increased to 1A with 
forced-air cooling.  I¹m sure these have failed owners at one time or another 
but they seem to have held up well for most 77/70 amp owners.  If mine ever 
blow, they¹ll get upgraded to slightly better specs at that time but nothing 
greater than the equivalent of six 1N5408 types per leg.

I¹m all for ³super-sizing² components, but not until a circuit¹s minimum
safe limits are calculated.    Over-sizing for the sake of over-sizing
seems like a lazy way to impress friends!

Paul, W9AC

-----Original Message-----
From: Manfred Mornhinweg <>
Date: Thursday, October 16, 2014 at 3:47 PM
To: Amplifier Mailing List <>
Subject: Re: [Amps] HV Diodes


 > Suffice it to say that the real world of tube type ham amps uses the
 > almost universally no matter what the configuration.

Do the Alpha 8410, 9500, 8406, and the 89 belong into the real world of tube 
type ham amps? I would say, they do. And they don't use the 1N5408 but instead 
use a potted bridge rectifier, rated at 5kV peak inverse voltage and 2A total 
forward current. I don't know with certainty what's inside it, but 4 strings of
5 each 1N4007 diodes would have exactly those ratings. Instead a bridge made 
from 1N5408 diodes would have a rating of 6A total.

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