Just to update my experience - I managed to complete and get my vibrato pedal working. The attached schematic has oodles of gain, with output starting to soft clip at 28Vrms and able to exceed 45Vrms with 20mVrms input. The vibrato uses a Magnatone circuit with cloned varistors. A 12Vdc plugpack allows direct powering of heaters, and provision of negative bias for the 12FQ8 triodes, and direct supply of a cheapo car inverter isolated dc/dc for 235V B+.
Although I only used two 12FQ8, and didn't tube roll others in, I did notice that the input stage 12FQ8 appeared to be sensitive to microphonic tapping or handling of the small diecast box that the pedal was constructed in, so there may be benefit in isolating the socket, and/or chassis. The input stage 12FQ8 was also very susceptible to stray hum coupling from nearby mains on the bench, and needed a full metal screen (eg. tube cooler) to suppress pickup.
Fixed bias imho was the simplest way to utilise the triode sections, as the common cathode can be simply connected to 0V. And for applications like the low frequency phase-shift oscillator, a common grid can be used with two separate anode circuits, and the high mu used to advantage.
