The PY800 was one of the last rectifiers of its type to be developed and is based on the PY81 from 1952. It was specifically built as an efficiency diode for television line scan in sets using 110° deflection angle tubes.
Considerable energy is fed to the line deflection coils and this has to dissipate during flyback. The efficiency diode channels this energy back to the supply rail smoothing capacitors for use on the next line scan.
The rectifier is specified as having a peak inverse voltage rating of 5,750 Volts, and a peak current rating of 450 mA. For sine wave use an input voltage of 1,500 Volts at 175 mA could be rectified. No voltage drop is quoted so the dissipation can not be given.
The anode end on. The inside of the two sheets is bright and the outside surface is blackened to radiate heat more effectively.
The insulated spiral seen emerging from the cathode circles round the heater and is connected to the anode. Pin 8 is given as an internal connection, in fact it connects to the anode. The heater is an insulated coil that is folded into two.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 74 mm tall.
References: Datasheet & 1040. Type PY800 was first introduced in 1961.