|Vibrato||7025 (1/2) 12AU7, 2 varistors|
|Output||30 watts peak (10 watts RMS)|
The 431 advances the circuit of the 421 by moving from the 6AV6 preamp to a 7025 based preamp and adding reverb. Like the 421, the 431 is a single channel amp with volume and tone controls. a single channel and tone control. Like the 421, the 431 has both tremolo and vibrato. The tremolo uses the oscillator to vary the bias of the power pentodes. A tremolo/vibrato switch moves the oscillator over to the two varistor based vibrato used on the Custom Series M4, M6, and M8.
The 432 was a 431 fitted with a 12" speaker.
The early amps had gold control panels, but this was changed to black in 1965. In 1966, the 431 became the 432.