The PY801 was specifically built as an efficiency diode for television line scan and the design dates to the early 1950s. 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 heater/cathode separator is the insulated helix seen held at the top. There is no electrical connection to the separator.
Made in England and the stitched anode.
The cathode tube with the hairpin heater in the centre and the separator wound round it.
The base of the cathode clearly showing the three components.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 71 mm tall.
