(Scientific?) Test of Battery Type and Voltage in a Fuzz Face

[Gus]

Something that might help is to make an LT Spice model of a FF
I would use the 2N2222 model it sims very close to what I measure when I build a circuit I simmed with a 2N2222
You can do a DC sim and see the voltages change at the transistors with different power supply voltages
You can look at the waveforms at different power supply voltages with the same input levels
You can add resistance to the power supply and change the input signal level.