Heater/Cathode Leakage testing

[bob91343]

It's a matter of the circuit and how much hum you are willing to tolerate. Each situation is different.

If I find a tube with noticeable leakage I try it and see if a problem arises because of it. If not, I use the tube. If I am working on a set for someone else I might be a bit more strict to avoid problems later.

[Alastair E]

For leaks H/C sometimes its possible to 'bias' the heater-chain more positive than the cathodes of the tubes, by about 30V--providing that one side of the chain isnt earthed to chassis .

The theory is it reverse biasses the 'diode' created between the leaky Heater and the Cathode.

This Ive done on a set some time ago where I couldn't easily get the valve to repair it properly.

It works fine.