Loud Humming goes away when i tap the tube

[Smienov]

Hi guys.
I have a crack i built in 2014, this has always been a problem but now decided i want to sort it out.

The amp works great but intermittently a loud hum will start, and i found if i just tap the tube with my fingers, it goes away, it may comeback in seconds, or it could be minutes.

Does this mean the tube is a dud or its a cold solder joint perhaps? Thank you.

[Paul Birkeland]

This is almost certainly a cold or unsoldered joint in the amp.