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[AMPS] 866A replacement .... SEMTECH STR4B32 ... any data please

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Subject: [AMPS] 866A replacement .... SEMTECH STR4B32 ... any data please
From: (skipp isaham)
Date: Sat, 29 Sep 2001 09:54:36 -0700
: From: "Wynand van Wyk" <>
: Hi all,
: I was today given two items at a flea market ... "you 
: are the only one I know that will appreciate and use 
: this in you amp projects" I was told. 
At a flea market, it's most often the first indication that 
one should look for the attached anchor chain... 
: It turns out to be two items with a 4 pin base (fits into 
: the 866A & 811A sockets) have hefty heat sinks and 
: anode cap on top.
: About as tall as a 811A tube.
: Markings ..SEMTECH STR4B32
: My guess it is a replacement solid state rectifier for 
: the 866A mercury valve rectifiers.
Not limited to the 866a replacement. There is a non 
mercury similar tube to the 866a which from memory 
is the 3B28 or 3B29.... one of those two numbers I 
Solid state replacements are/were very popular as a 
viable retrofit in tube power supplies.   One must 
consider the original 866a has quite a bit of voltage 
drop while in operation. Same with the non merc 
tube (and most tube rectifiers).  
It is interesting to know that some mfgrs often relied 
on the voltage drop as part of the circuit parameters. 
Replacement of the tube rectified raises the supply 
voltage, sometimes too high in certain circuits.  There 
have been failures from the elevated supply voltages. 
For a block of time, equipment owners were replacing 
vintage vacuum rectifiers with the ssr replacements. 
Most "get away" with the higher output supply voltage. 
They are made in all sizes and types, you happen to 
have a common HV SSR 4 pin unit.  They are also 
manufactured for smaller supplies and popular in 
some Collins Amateur Equipment. 
Some of us pull them back out of our amplifiers to 
restore vintage operation.  In the tube guitar amplifier 
groups I frequent, we consider the "sag" (operating 
voltage drop) a feature.  :-)  They do offer a measure 
of ruggedness and reliability vs glass packages. I've 
never had one fail. There is a very slight increase in 
amplifier power.  Extreme or marginal circuits might 
require adjustment of the zsac value. 
I now run the non merc version in my 30-S1, the SSR 
units  work and work in lower profile power supplies 
(which are viewed less often).   Original 866a's 
still glow in circuits that allow their operational view
from a safe position.  The Viking Valiant is such an 
I'll look to see if I have a data sheet for your particular 
ssr replacement. 
: Any info and how I can utilize this in my High Voltage 
: supplies appreciated.
: Wynand

Most of the installation instructions are basic plug & 
play, but some are smart enough to advise caution 
related to the resultant elevated supply potential(s). 

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