[Amps] 3-500Z short / fix?

Robert woodr90 at gmail.com
Mon Jul 27 20:46:57 EDT 2020


while repairing Zener diode - pulled two 3-500 Eimac tubes 

one had short (all five pins read zero ohms to any other of the five pins)


took shorted tube to shop for a photo.   sell tube as sample/light bulb.



there is my old, really old car battery charger

tube is bad so why not

place battery charger in 6Vdc position

there are no protective shutdowns in this charger

(multi-tap transformer & one diode) 

one clamp on two filament pins

other clamp on grid pin

let's see if grid will "melt" at area of the short


small glow/flash inside - then battery charger current drops to zero

go to 12vdc, no current 


Measure ohms at tube pins:

filament good

Grids all connected

No short between filament/grid


shake tube - still OK

shake tube while measuring ohms, still OK


so, do put 3kV on the plate and see what happens??


anyone tried this before?

AL-82 test bed





Midland, Texas


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