G'day Jack.
I have cleared a grid to filament short with a 100,000uF electrolytic
capacitor charged to 13.8V from my shack power supply. The charged
capacitor was connected between grid an filament and it blew away the
short.
I don't have a hi-pot tester but the tube looks fine on my 1000V Megger.
I did this about 2 years ago and to this day, I'm still too chicken to
put the "fixed" tube into my amp and fire it up, so I can't tell you if
the tube is usable or not.
73, Alek.
VK6APK
On 12/06/2016 12:55 AM, Jack C. Shutt wrote:
Hello all. I don't post here very often, but always enjoy reading the posts
and comments about the experiences of others.I'm looking for some info and
advice on 3-500Z tubes. I have used these tubes for many years in several home
brew amps, as well as in a few commercially-built units. I recently have had
some bad experiences with bad tubes (fil to grid shorts?) resulting in the loss
of some expensive components such as the fil/bias transformer, grid meter, and
bias circuitry consisting of hard-to-find high power zener diodes, etc. I'm
wondering if anyone has had any success in reviving bad tubes with shorts. Is
there a procedure that can be used for clearing these shorts? Also wondering
about design additions that you may have included in amps to protect the
circuitry from catastrophic failures. I have experienced failures of Eimac
tubes and Chinese versions. Looking forward to your comments. 73, Jack, W9GT
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