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3/10/18

PULTEC EQP-1A POWER SUPPLY SCHEMATIC

The Pultec EQP-1A circuit draws approximately 20mA from the power supply. The total circuit current is the combination of the 12AX7 plate currents, 12AU7 plate currents, 12AU7 grid bias current, and the Heater DC network current. Back when I taught electronics I sometimes used this schematic example as a test question.

trenton blizzard pultec eq power supply schematic

My Pultec EQP-1A power supply schematic is shown next.  Note: heater connections are not shown. This schematic shows how I wired the Hammond 270FX transformer. The two green (GRN) heater wires connect to all heaters.

12AX7 / 12AU7 HEATERS

Since the 270FX heater voltage winding is 6.3VAC, you need to connect the heaters on the 12AX7 and the 12AU7 in parallel by connecting pins 4 & 5 together on each tube. You then connect one green wire to pin 9 (center-tap) and the other green wire to pins 4 & 5.

6X4 HEATERS

For the 6X4 tube, you connect one green wire to pin 3 and the other green wire connects to pin 4. The 6X4 tube does not have a heater "center-tap" pin. The +60V on the green-yellow (GRN-YEL) wire floats 60 volts on the heaters and helps reduce cathode to heater potentials which can extend tube life.

trenton blizzard pultec eq power supply schematic

Thanks for reading,
Trenton

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