David Looser wrote:
"Patrick Turner" wrote in message
...

Ian Thompson-Bell wrote:
I often see volume control pots with their wiper connected directly to
the grid of the following tube. Trouble is as they wear they get a bit
scratchy and often lead to the grid becoming disconnected. Would you
agree it is good practice to add a resistor (say 1Meg) directly across
the grid?

Cheers

Ian
Yes. From 0V or bias voltage to the grid.

AND better you replace the pot after cleaning it if that doesn't stop
the sratchiness.

And I would also suggest ensuring that there is no DC across the pot (such
as that due to a leaky coupling cap from a previous amplifier stage). Even a
pot in pristine condition will create noise when adjusted if there is DC
across it.

David.



Yes I have come across that on old broadcast receivers. Leaky coupling
cap buggers up grid bias on output tube - result distortion and hot
tube. often need to replace cap and tube to repair.

Ian