D5 & D6 did their job. Replace them, check that R3 isn't open, and verify you
don't have a gassy tube(s). 3-500Zs produced after 1985 by Eimac are noted for
having poor wire-glass seals (see
leak. All Chinese-made tubes are suspect of not being pumped down as much. In
both cases, they become gassy prematurely. Hi-Pot your tubes to verify they're
alright BEFORE applying full HV. If one or both fail, you can try gettering
it/them. If still NG, it's time for new tubes.
Please refer to the emails I sent direct, the last one on 10/17/16.
vy 73,Bryan WA7PRC
Date: Mon, 4 Oct 2016 23:45:38 +0000 (UTC)
From: Catherine James <email@example.com>
Subject: [Amps] SB-220 Harbach meter board - blown meter diodes
In the continuing saga of the "new" SB-220...
I've opened everything up and it looks good to me. No burned spots, signs of
arcing, etc. A previous owner has already installed the Harbach soft-key and
soft-start mods as well as the Harbach meter diode board, and it was clearly
done a long time ago since the PC boards are not the modern green type.
I have replaced the PS capacitors via the new Harbach board.
Unfortunately, it appears that D5 and D6 on the Harbach meter board are blown
(shorted). The long string of 1N5408's check out fine.
Any thoughts on what else I should check or replace that may have been taken
out when the meter diodes went?
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