Divining intermittant cathode-heater leakage?

For intermittent tests, you'd like to tap the tube (use a wooden stick). My preference would be to test with cathode warm, using a neon lamp and limit resistor to a plate supply (200V or so), returned to the heater.

An intermittent will make the lamp flash, but it isn't clear what, if any, motion you'd see on a meter needle. Leakage (like a gassy tube) might cause some flicker, too.

For intermittent tests, you'd like to tap the tube (use a wooden stick). My preference would be to test with cathode warm, using a neon lamp and limit resistor to a plate supply (200V or so), returned to the heater.

An intermittent will make the lamp flash, but it isn't clear what, if any, motion you'd see on a meter needle. Leakage (like a gassy tube) might cause some flicker, too.

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you wouldn't happen to know what effective leakage resistance in say ECC83 starts to make its presence felt audibly on the output of an amp? I find neons rather temperamental and not reliable in DC situations. There is a mains neon on my bench ps that rarely lights unless the room light is very dim or off , very odd. If the ps packs up then I will sort that and the neon while in there

Can't help you with a TEST, but I've had success blowing out shorts, intermittent or otherwise, with a stun gun.

At >25M, you're gonna need to look for issues with the socket and the circuitry hooked to it. Doesn't take a very big spider web or chunk of damp dust to make

I once had a spider build a tidy web across a CDROM read lens...but that's another story.

YMMV

Your copy of Outbreaks In Excess is missing an important patch.