I take it that you don't have to use negative supply if you are NOT trying to emulate some known amp. In fact in this JCM800 emulator only three first gain stages actually use additional negative biasing.
I believe the last two stages are just buffers (source followers), so they don't really affect the distortion sound, right?
How about using a lower supply voltage in range of 48-100V?
I tried this at 120v and seems to work OK with about -2v bias, but I don't have a scope to check curves:
Rg 1M+47k,
Rp 100k,
R2/
D1 1k/I.R. LED,
R3 330R (but I'll probably change to 220R later),
D2-
D4 1x 1N4007,
LeftR 1k5,
RightR/
C2 1k/220nF.
Wonder if an I.R. LED for D2-D4 would work OK as well? I'm not really looking for an authentic replication of a certain amp's sound, I just want decent overdrive/good voltage swing. Most of the distortion I want will come from the power tubes anyways (6AS5, 8K P-P, fixed-bias -13v).
I also would like to point out that I used a "sourcedyne" (split-load) inverter in my prototype, with 47k for both upper and lower loads, 1k source resistor, 10k stopper and 470k Rg. B+ at 125v.
Maybe there's a way to get a more plesant distortion curve in that inverter as well?