To use the tremolo stage as a gain stage:
1)Connect the bias feed from the output tube grid leaks directly to
ground-- if the output stage is cathode biased; or directly to the bias
supply-- if fixed biased.
2) Remove the 20nF cap from between the Speed/10nF/20nF node and plate of
the tremolo stage
3) Connect the wiper of the Intensity pot to the 10nF that feeds the splitter
4) Lift the 3M3 and 10pF from the above junction, and connect them to
Spped/10nF node.

The Speed is now a tone control and the Intensity becomes a master volume.
To give this control a more "logarithmic" feel, add a 25k between the wiper
and ground.

Over-all, this mod produces a warm overdrive, depending on the pickups on
your guitar-- good for jazz or blues.