[Amps] 3-500Z tube problems

[Jack C. Shutt]

 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