From MetroAmp Wiki
Metroamp replica of the Drake 1203-80 power transformer in a horizontal or "laydown" mounting style. Hense the "ML" suffix.
Primary 120, 220 and 240V AC, 50 or 60Hz operation
6.3V AC @ 8A heater supply
95V AC bias supply
high voltage supply with 80% taps for voltage switching option (as used in Metroamp 12 Series amps).
Typical B+ voltages: 490V (full secondary), 400V (80% secondary taps) rated at 450mA.