Part 5: The power transformer POW80 of The Vanderveen Project

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The sizes of the POW80 and GIT80 transformers are equal. At the primary side mains voltages of 100, 115, 200, 230-240 V (50 or 60 Hz) can be connected. An electrostatic screen stops disturbing signals from the mains. The two windings of 270 V are for two separate high voltage supplies. The negative control grid voltage is delivered by the 50 V winding, while the filaments of the tubes are powered by the 6.3 V winding.

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The circuit diagram of the power supply is not complex. In the mains a fuse and an on/off switch are placed. The metal case is connected to the ground of the mains, as is the electrostatic screen. Each high voltage winding is fused while they are switched together (bypass function), followed by rectifying van buffer capacitors. The two resistors of 100 k discharge these high voltage capacitors in the bypass mode. This is a very important safety precaution during experimenting. The 50 V winding is followed by rectifiers and buffered. This voltage is intended to adjust the quiescent currents of the power tubes. The 6.3 V filament voltage needs grounding, which is done with two resistors.

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