Power Amp Grid Leak Resistors

[mwelch55]

I noticed in this schematic, there are 100K grid leak resistors instead of what I normally see in Marshall amps (220K).  This schematic is from the power section of the Fortin Cali Mod (which is a modded Marshall).  The Ceriatone Chupacabra uses 110K resistors in this position. 

What is the advantage/disadvantage of using a smaller value resistor?

[SILVERGUN]

Lower value = more load on PI and less drive on power tube grids
Higher value = opposite

[tubeswell]

Its a balancing act. Lower grid leak resistance means a better grid leak pathway to replenish electrons lost from the control grid as it heats up. But this happens at the expense of impedance bridging (because input impedance is lowered relative to output impedance from the driving stage/PI), resulting in more signal attenuation than what you'd get with higher value grid leak resistances.

[PRR]

> advantage/disadvantage of using a smaller value resistor?

It is closer to the Rated MAXimum grid resistance for fix-bias EL34.

[mwelch55]

Would a lower value affect the tone of the output tubes, or just attenuate the signal going to them?

[PRR]

It has to be considered in context of the WHOLE circuit.

[timbraun]

The Marshall schematic for the JMP 100 shows 120K grid leak resistors for the EL34 model, and 82K for the 6550 model. FWIW

http://el34world.com/charts/Schematics/files/marshall/Marshall_jmp_superlead_100w_1959.pdf