Yes.
Yes, eventually.
No, it is in shunt with the signal, not in series with it. The bigger the shunt resistor, the less the attenuation, and the lower the thermal noise contribution. 1Meg is good.
The pot will eventually scratch with or without the resistor. To stop DC getting to the pot you need a capacitor as well as the resistor. The resistor on its own merely protects the valve from losing bias when the pot fails.
1M is good. Don't make it smaller. You could make it slightly bigger.
1M is good. Don't make it smaller. You could make it slightly bigger.
+1
My bad, I missed that 1M resistor provides bias, too. It is essential for a proper working of the amp.
In this case, it's simply a guard resistor in case the wiper lifts inside the pot. Even better would be to use a 100K linear pot and make the resistor 16K8. That gives a log response, and linear pots don't have the problems that seem to plague log pots.
The problem with loading a linear pot to simulate a log pot is that it makes the poorest resistor in the system (the track-wiper interface) a non-trivial part of a potential divider in the signal path.
With a direct connection, as shown, the 1M does not provide bias except under fault conditions.
With a direct connection, as shown, the 1M does not provide bias except under fault conditions.
I habitually use 2M2 as the grounding resistor at the inputs of solid state gear.
I have a valve/tube preamp and the manufacturer recommended removing the 1M grounding resistor located before the DC blocking cap to leave just the grounding resistor in the Source. They claimed the slightly higher impedance at the input improved performance.
It seems that very high input impedance can be an advantage, if the Source to Receiver interconnect is actually connected.
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