>Greetings,
>
>I suspect that one or both of the 3-500z's in my SB-220 (original Eimac
>bottles, date code 1977!) may have a grid to filament short. I've
>measured about 11 Kohms with my DVOM while the tubes are still in the
>socket. I've heard that I should be seeing around 100 Kohms.
>
>Can someone confirm what the grid to filament resistance of a good
>3-500z should be?
It should be very high - with the valve "cold". With the valve warm, it will
presumably be just like a diode and the resistance you measure will depend
on the polarity. However, 11k is high enough as the 3-500Z is zero bias. Are
you sure you are not just measuring something in the PSU ? There needs to be
some path from Grid to Cathode after all.
Is there some fault ?
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