Grid stopper value in Mesa: 3.3M ??

[balokker]

Not sure what this 3.3M resistor is doing here in this Mesa Nomad 100 head. Other similar Mesas (Dc5, Dual Rec) have nothing here. Is this functioning as a grid stopper?

[Enzo]

Forms voltage dividers with the gain pots and resistors to the right of the cap.

[balokker]

I jumpered a 100k in parallel with it and heard zero audible change.

[Pedro Vecino]

That resistor is between the contacts of the relay that divides the blocks of channel 1 and channels 2/3 at input.
When channels 2/3 are activated, resistor is short-circuited. When channel 1 is on, it is active, but channels 2/3 are muted later. I imagine it is to avoid a part of noise in the switching between both blocks

[balokker]

Thanks I see what you mean. It looks like it's bypassed in either channel 1 or 2-3...

[Gingertube]

It is just there to keep the 0.02 uF cap at the anode voltage so you don't get a pop when the relay operates and connects that cap to the anode directly.
Cheers,
Ian

[R.G.]

As a bit of back-up theory, grid stoppers only exist as such when they're attached directly to the grid of a tube, and in the physical (as opposed to schematic world) they only work as intended when they're as close to the grid socket pin as it's possible to get the body of the resistor.

This is because a grid stopper is intended to form a lossy low pass filter in combination with the real grid-to-ground capacitance and the virtual Miller capacitance to the plate. Grid stoppers are normally intended to stop very high frequency oscillations, and in that realm, moving them even a fraction of an inch away from the tube electrode may have ill effects on what the stopper was supposed to do.

So, by inspection of the schematic, no, it can't be a grid stopper because it's not connected directly to the following grid. The other comments are exactly correct for the actual function of this resistor.