Here’s a quick post about the other day, fiddling with my 1930 homebuild radio.
A couple of things happened:-


1 I was able to get it to work much better after modifying it’s circuit a little bit with a different grid leak resistor arrangement.
2 After returning from a nice walk with the better half, I’d discovered that the radio barely worked at all with virtually no volume.

I was quite miffed at 2, and spent much of the remaining day debugging it. It all turned out to be caused by corroded and loose contacts in a sprung valve holder. Anyhow, I won’t bore you with any more detail other than it took ages to strip and clean all the small components that make it up.
Before and after pics below

Before
After


These holders are designed to reduce audio vibration affecting the operation of the valve and are called ‘anti-microphonic’ valve holders.