Now I started this post before I read MJMPs
...
Hey RG, ok simple answer (and I have some sympathy for Kims suggestion BTW).
After a couple of wines and a cigarette and some contemplation (and a ~decent gawk at the schematic (to the extent I understand circuits
not nothing but not something MJMP ish).
My gut feel (and I hear you, you like it) is chuck in a couple of Mullard LPs and wind any gain trimpots back a bit (if you can/and they exist) and it might just do the trick.
Now taking a more "lets try to understand the circuit" approach... seems to me there is a fair bit of stuff happening in the V1 stage between T1-A and T1-B triodes (do you remember a 12AX? tube has 2 gain stages ie 2 triodes ? I'm hoping MJMP will chime in and save me here LoL). You'll notice (I hope) on the schematic how each triode of each tube is depicted (T1A & T1B, T2A & T2B and you can see how they all (each triode) gets power from the power supply (so how a tube and/or to some extent a transistor work is you give them some power then you use a lower level input signal to control its (the power) flow to the output (more signal more output
))). T1's circuit is more complicated (I'd proffer in here lies the squish (and
the place to change/vary/fix it) and T2 is basically just a more (even) gain stage (it's way less complicated).
Now to vary the squish (if I'm right) I've thought of 2 approaches (just changing tubes). You could go for a lower gain V1 tube (so if squish is triggered by signal threshold (like a compressor) and less signal is coming from T1A because of lower gain tube, it may not be triggered/exceeded quite as much ? (so a 12AT7 or probably better
a 12AU7) Gain of 70ish or 50 ish mu (12AX7's are 100+ mu
and why we like them LoL) . The squish is triggered by something (and changing whatever that is is also an option).
The other approach is just use really open headroomy tubes and keep the gains down a bit ? Again the Mullard LPs are good for this (they are highly recommended for HiFi Audiofile applications) but there are others as well.
An aside.. when you look at the schematic and see the circuity around the 4 triode stages, this is also how our beloved ADA preamps work. The various "voices" in MP-1/2, Classic and MB-1 alter things in these circuits (between the 4 triodes) to create the basic tones.