The circuit uses a ECL82 tube, which is a triode and a pentode in one, whereas the triode is used in the first stage and the pentode in the power stage of the amplifier. At the output, an output transformer from an old vaccum tube radio is used to adapt the amplifiers high impendance output to the low impendance speaker. The power supply delivers around 6V which go unrectified to the filament of the ECL82 to heat the tube, the PY88 filament needs 30V which it gets from the anode voltage with a resistor. The anode voltage of 40V is rectified by an PY88 Diode and filtered by a big cap to supply the amplifier. The potentiometer at the input sets the gain, so I had to test a little bit to find a compromise between volume and distortion.