Conductive circuit board?

[Helmholtz]

Ok. But you can still measure DCV on grid pins, right? I mean, it couldn't be that what your meter is reading is not accurate because of board resistance, is it?

Sure, you could see increased voltage at the grid. In my example a 1M meter would read 0.5V while a 10M meter would read almost 1V.

But the main difference between meters shows when probing the board between eyelets.
When a 1M meter reads 0.5V, a 10M meter will read 5V because of the huge "source" resistance of the board.
Always good to know the input resistance of your voltmeter.
I typically use a 10M meter, but most non-professional meters are only 1M.

I guess another issue could be AC voltage. If there are large voltage swings at tube plates and the board is conductive then these swings might still be transferred intermittently (cycle peaks) to other circuits. This wouldn't be seen in any static testing.

AC board resistance can be assumed to be the same as DC board resistance.
So static voltage tests are a good indicator of possible problems.

[stokes]

"When a 1M meter reads 0.5V, a 10M meter will read 5V because of the huge "source" resistance of the board."
So which can be considered the correct voltage? I just checked and my Fluke has a 10m input impedance and I see .5 vdc is it actually a half volt or is it .05 v's?

[Helmholtz]

"When a 1M meter reads 0.5V, a 10M meter will read 5V because of the huge "source" resistance of the board."
So which can be considered the correct voltage? I just checked and my Fluke has a 10m input impedance and I see .5 vdc is it actually a half volt or is it .05 v's?

As said a higher resistance meter will give a higher reading. There is no "correct" reading. Any meter just shows the voltage drop across its input resistance. You would need a meter having an input resistance of several Gigaohms to read close to the actual voltage on the board between eyelets.

A 1M meter would read 0.05V in your case.

I'd say a 0.5V max. reading with a 10M meter shouldn't be a problem, as it means that the grid voltage in my example could only be raised by 0.05V.

OTOH, a 1M meter reading 0.5V would indicate critical board conduction. Depending on where on the board this is measured, it might upset the circuit.

[stokes]

Thanks, Helm

[J M Fahey]

You narrowly focused on the board.
My suggestion: REPLACE THOSE POTS.

All of them,do not waste time in doubtful "cleaning".

The board is the least of your problems.

Also those Bright slider switches if present.

Other jacks can be cleaned, although replacing wouldn´t hurt either.

[stokes]

JM, not really focused on the board, I am aware of the likely faults in this amp and am still sorting things out. I have never experienced an amp with an actual conductive board and seeing as how this amp was exposed to extremely humid environment, evidenced before I even opened it up, I had to consider it a possibility and just wanted some opinions on the issue.

[gbono]

You can try using fish paper (transformer) paper under the fiber outlet boards.