The PY81 was specifically built as an efficiency diode for domestic television receivers with series heater chains. 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 EY81 does the same job for professional monitors that feature an isolated chassis and mains transformers for parallel heaters.
The nickel sheet anode is blackened on the outside. At the ends the inside of the sheet is exposed as it forms an extra heat singing flange.
Face view with the two anode halves stitched together.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 72 mm tall.
Reference: Data-sheet. Type EY81 was first introduced in 1958. See also1958 adverts.
