P.I. grid leak question

[joesatch]

in this schematic why isnt the circled 470k resistor 1M ?

[sluckey]

Most likely a draftsman oversight. I don't see any special mojo going on.

[pdf64]

I recall reading an interview with Steve Grindrod, in which he seemed to indicate that kinda thing was beneficial in preventing power amp overdrive asymmetry.  https://el34world.com/charts/Schematics/files/Park/Park_1210_1240_rock.pdf

[shooter]

beat me ^^

I don't see any special mojo going on.

I was thinking it would "add" asymmetry into the mix??

[stratomaster]

If I recall correctly Mesa Boogie uses 330k/1M in that same spot.  I don't know that it actually makes a difference, but I think the theory is due to bootstrapping of the input impedance there is an asymmetry for each triode. This can affect overall low end response each triode in the PI.  By having different resistors as grid leaks this difference is minimized and balance is restored to the world.  Essentially a frequency response version of what the 82k/100k plate resistors are doing to the voltage gain.  Given a sufficient input cap I don't see how this makes a bit of difference. 

[Latole]

There are many resistor value you can use .
Some Traynor amps use 68K, some Marshall 1 meg some Fender 220k .........

[HotBluePlates]

I was thinking it would "add" asymmetry into the mix??

The long-tail is already unbalanced, cause "reasons."

That's why they use non-equal plate load resistors to attempt to restore the balance.  But Aiken has noted the right values to achieve balance are not as-far-apart as the 82kΩ/100kΩ commonly used (which are commonly used because they're part of the 10% tolerance E12 series that were cheaper once upon a time).