The PY81 was specifically built as an efficiency diode for domestic television receivers with series heater chains. The EY81 does the same job for professional monitors that feature an isolated chassis and mains transformers for parallel heaters.
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.
This Mullard exhibit is marked as Foreign Made and also Made in Italy.
The stitched anode.
The Made in Italy can be seen on the lower right of the image. At the bottom of the cathode tube can be seen the two insulated heater strands. The heater is kept away from the cathode tube walls by an insulated wire helix.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 73 mm tall.
Reference: Data-sheet. Type EY81 was first introduced in 1958. See also1958 adverts.
