value of grid to ground R in SE amp

[tubby]

hi all,

i'm trying to tweak my SE amp circuit for max. vol and tone.
so i was wondering if there would be any noticable difference in vol. or tone
if i change the value of the grid to ground resistor going to pin 5 of the power tube.
at the moment this is a 220k. output tube is an el34 / kt88, cathode bias. i'm considering 470k for starters.
any experiences?

[stokes]

hi all,

i'm trying to tweak my SE amp circuit for max. vol and tone.
so i was wondering if there would be any noticable difference in vol. or tone
if i change the value of the grid to ground resistor going to pin 5 of the power tube.
at the moment this is a 220k. output tube is an el34 / kt88, cathode bias. i'm considering 470k for starters.
any experiences?

It will allow more of the signal to get to the grid of the power tube,could be a bad thing tho.Too big a signal could cause grid clamping (bad) and/or the power tube to go into saturation sooner,which may or may not be a bad thing.Tweaking the current draw of the power tube may help,but that would likely bring you back to where you were with the 220k anyway.Try it and see if you like it.Some master volumes are basically a variable grid resistor here.

[tubeswell]

Or you could try some of the AX84 SE power amp options. (Most of them don't have a grid leak resistor there, they have a 1M MV pot instead - and a grid stopper)

[tubby]

forgot to mention that there is a 1M MV in front of the 220k.

anyways, just looked up the specs on a k88 data sheet:
the ground reference should not be larger then 270k
if the tube is biased at a dissipation of more than 35W (i was aiming at around that dissipation).

so i was thinkin....
since i'm using 220k now, i guess there won't be any noticeable difference caused by those 50k. on the other hand i'm using only half a 12ax7
to drive the KT88, so maybe i could get away with using 470k and not having blocking distortion. if anyone has experience with that kinda specific issue,
i'd be glad to hear it, otherwise it's gonna be trial and error

[tubeswell]

If the 220k and the 1M pot are in parallel, they make 180k at the most. Whereas if you used 270k in parallel with the 1M pot, you would get 212k between them when the pot was maxed out

[Jag]

If you still want the MV and you have a 220k in parallel with the 1M pot, like Tubeswell described, I'd remove the 1M pot and replace the 220k resistor with a 250k pot.