Heathkit SB-400 Neutralization Procedure

[Glen Zook]

Although I usually neutralize my SB-401 using the
method in the book, I want to comment on which type of
tubes you replace the finals:

Unless you want some pretty "hairy" experience with
neutralization (and they may or may not neutralize) do
not use 6146B tubes or any 6146W tubes with a "code
date" later than 1964 (which are basically the same
tube as the 6146B).  Sometimes the 6146B works in
equipment that was originally designed for the
6146/6146A/8298 series, but using the 6146B/8298A
often results in all sorts of problems.

Collins ran into problems with the neutralization
circuitry actually "burning up" in the 32S-1, 32S-2,
32S-3, 32S-3A, and KWM-2 series when the 6146B was
substituted.  Since the military had the requirement
that the 6146B types be able to be used Collins had to
redesign the neutralization circuitry.

The article that appeared in Electric Radio a couple
of years ago on the 6146 family of tubes and was
reprinted by the Collins Collectors' Association
several months ago can be found on either website that
appears at the end of this message.

The 6893 series of tubes which are basically 6146
tubes designed for 1 KW input pulse service can be
used inplace of the 6146 / 6146A tubes without any
problems.  The problem with the 6146B tubes is that
they are really a different tube with higher plate
dissipation ratings, different screen requirements,
and different bias requirements.  When RCA first came
out with the tube they stated that it was basically a
"drop in" replacement for the 6146 / 6146A.  However,
this did not prove to be true!

Glen, K9STH




--- Wayne Mackin <wmackin at ROGERS.COM> wrote:

I'm about to replace the 6146 finals in my SB-400, and
was wondering if there is a procedure for neutralizing
the transmitter that does not require disassembly of
the unit and unsoldering of components? (the only
procedure in the manual is done before final assembly
of the TX).

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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