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[AMPS] advice on an old SB-220

To: <amps@contesting.com>
Subject: [AMPS] advice on an old SB-220
From: ccc@space.mit.edu (Chuck Counselman)
Date: Fri, 10 Nov 2000 16:54:00 -0500
Eric Moore <emoore@windemullerelectric.com> wrote:
>...The tubes test good, but could they be gassy from sitting all of these
>years? I am not very familiar with 3-500Z's, will letting the filaments
>heat, and just sit there for a few hours, cooking, de-gas the tubes if they
>are gassy?

This is as much a question as an answer, but FWIW:

I know nothing about 3-500Z's, but a close friend and co-worker
successfully degassed quite a few 50-year-old (WW II vintage) 807's and
other relatively small tubes by letting them run with (controlled) plate
current.  First he ran them with just their cathodes heated; but nothing
happened.  Then he applied B+ (a few hundred volts) and adjusted the grid
bias to set the plate power dissipation to a healthy but safe level -- and
the tubes degassed themselves within a day or two IIRC.  Whether this
technique will work with a 3-500Z, I don't know.  Perhaps in an 807 the
gettering material is applied to the plate, so it works when the plate is
hot.  I have no idea how a 3-500Z is gettered.  Is its plate metal?  Is the
outside of the plate gray?  If so, that might be a getter.

73 de Chuck W1HIS



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