How to power up an old unknown quantity tube amp?

[Ian444]

I lucked across a variac in an unused piece of test equipment at work, an old circuit breaker tester that was supposed to be disposed of. With a couple of ebay Chinese panel meters, a 1A circuit breaker, a 240V wall outlet and a few hours I made this "thing". Thanks very much for your help and suggestions guys. Much appreciated.

[turbo5speed]

Have a really good look at the tube side of the power tube sockets and look for carbon traces.

Just out of curiosity, what is the cause of those carbon traces?

[Structo]

Arcing.
When a power tube shorts it is usually the plate to heater and it leaves the black carbon track from the arcing.
It is near impossible to clean it well enough to remove all the carbon but some times if it is light enough you can get it off.

Best course is to replace the socket.

[turbo5speed]

Makes sense. Thx mate!