I'm talking about when it doesn't matter to them. The only case: when there is no outside connection provided.
So if you build something with a speaker jack you have to ground. But if you are doing something like turning an portable tube radio into guitar practice amp, you need to ground it or check that it is grounded. Because you are adding outside connections.
And they all do - at least everything I've designed... They are even all connected to the same branch circuit.
I remembered a DIY amp come to me to be modified because some sound engineer got it and want to use it with balanced equipment, and it oscillated without anything connected to its input. Is there some sort of school of though in the DIY world for not having a the grid bias resistor in? (grid to ground) because that is what I found on that.
Grids must always be referred to a DC potential, under any and all conditions.
But the inputs should always be either connected, or shorted to ground, when powered.
But the inputs should always be either connected, or shorted to ground, when powered.
I guess it was just something particular to that builder who made that capactron tube amp then. In the end, I did that by installing a wide band signal transformer with input termination so it would work with balanced monitor controllers.
Some people think it's unnecessary because if there's a source connected it's fine... I generally use RCRCR on the input like follows: 100k -> 0.033µ -> 1M -> 0.22µ -> 510k. That tends to keep the nasties out (ELF).