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Stereo vacuum tube audio amplifier

     This simple stereo vacuum tube amplifier is using ECL (parallel) or PCL (serial) tubes. They contain preamplifier triode and power pentode in one tube. Vacuum tubes like PCL82, PCL84, PCL85, PCL86, ECL82, ECL84 or ECL86 can be used. I used PCL82 tubes with 16V 0.3 A heaters and an anode loss 7W max. The amplifier is powered from the mains transformer. Filament voltage selected according to tubes (for me 16V 0.6 A). Anode voltage of vacuum tubes is not critical, may be about 100 - 200V according to the desired power. More voltage gives more power, but the tubes will have highrt anode loss and higher current, which causes faster wear. Filtration with two separate 100uF capacitors with a resistor between them is required to better filtration (eliminates hum). Capacitor 22uF is an additional filtration of voltage for preamplifier stage, which is most sensitive to the voltage ripple. The speakers are connected through the vacuum tube output transformers. The input is going through stereo (double) logarithmic potentiometer for volume control.

     Warning! Operating voltage of this vacuum tube amplifier is dangerous! Prior to manipulation, it is always necessary to disconnect it from the network and make sure that the capacitors are discharged.

Stereo vacuum tube audio amplifier schematic

Completed vacuum tube audio amplifier in wooden box.

The electronics.

Heating tube.