The PY800 was one of the last rectifiers of its type to be developed and is based on the PY81 from 1952. Here the design has equalised and both PY81 and PY800 appear on the glass.
This half wave rectifier 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 anode parts are stitched together.
The cathode connection ribbon connects to the top cap. As the valve was designed for series heater chains the heater cathode insulation has to withstand several thousand volts on each pulse. The insulated helix emerging from the cathode tube keeps the heater well away from the cathode walls.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 73 mm tall.
References: Data-sheet & 1040. Type PY800 was first introduced in 1961. See also1961 adverts.
