[Amps] 3-500Z tube problems

[Alek Petkovic]

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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