Stout MV ?

[Madison]

I'd like to use a "type 2" MV on a Stout.
Can I just use a dual ganged 500K in place of the 470K resistors?
Thanks

[HotBluePlates]

Sure you can.

You may want to have a resistor from ground to wiper on each section, as insurance against the wiper becoming intermittent. It would keep the tubes from losing bias but only becomes a factor when the pot is worn out or defective.

Ideally, you'd like to not change the apparent resistance of the master, so a resistor around 10 times the value of the pot would be right; 4.7-5M ohm. But that's pretty big if the wiper does open up, and could result in some loss of bias due to output tube grid current. I don't know the best compromise off hand, so if anyone has more experience or a better suggested value (maybe 1M or so), I'll defer to them.

[Shrapnel]

I think a good solution would be, keep the 470k grid resistors in place, and use a 1M pot with the wiper in parallel. That way, you'll never be over max recommended resistor from grid to ground should the wiper lose contact, and yet, at max volume, the grid will still be happy. IOW, leave the original resistor alone, and put the pot in parallel.

[HotBluePlates]

The problem with that is that it reduces the gain/output of the phase inverter.

We normally think of the plate load resistor as setting the operating point and gain of a tube stage. While it does set the d.c. operating point, the following stage's grid resistors are connected by the coupling caps. So at a.c., the load looks like the plate load in parallel with the following grid resistors to ground. That reduces the gain to an a.c. signal for the stage ahead of those grid resistors.

Naw, I guess on second thought (you gave me a good one), use a 1M ganged pot, and 1M resistors from the wiper to the ground lug of each pot. Full-up, the combo looks like 500k (same as stock), and at any lower setting it will look like less to the tube. It will only look slightly low to the phase inverter at settings below max.

That will also allow the existing coupling caps to keep essentially the same response.

[Madison]

>>leave the original resistor alone, and put the pot in parallel.

Yes, this is exactly what I am doing now and iit seems to work fine.
Just wanted to be sure it was the right thing to do and a tasty way to do it.

Thanks guys  for the advice.