Marshall jvm410h problem

[Rod]

Well it seems that something its wrong with the R91, 1 Mohm resistor as you can see in the video bellow, the resistor started to measure 0.5 Mohms. With the probe at 1X , im still having the drift

https://drive.google.com/file/d/1aUC...ew?usp=sharing

Should work the same. Exact resistance is not critical.

[Helmholtz]

Well it seems that something its wrong with the R91, 1 Mohm resistor as you can see in the video bellow, the resistor started to measure 0.5 Mohms.

No sense measuring resistance with a signal present (or the amp turned on).

If you don't trust the resistor, replace it.

Did you ground your scope probe at the amp?

What is your signal level?

[Mick Bailey]

You could experimentally tack a 1M resistor directly from the grid's solder pad to ground to see if that gives an improvement in stability.

[Rod]

Of course i grounded the scope at the amp chassis. that resistance was measured with the amp off. the signal its at 150 miliVolts.

No sense measuring resistance with a signal present (or the amp turned on).

If you don't trust the resistor, replace it.

Did you ground your scope probe at the amp?

What is your signal level?

[Helmholtz]

Any signal is likely to disturb the Ohmmeter.

At what DC voltage does the grid stabilize? You should be able to read that from your scope.

Please answer all my earlier questions.

[g1]

Are preamp tube sockets mounted on the circuit board in this model?