The U153 (almost = PY81) 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 rectifier is specified as having a peak inverse voltage rating of 4,500 Volts, and a peak current rating of 450 mA. No voltage drop is quoted so the dissipation can not be given.
This other exhibit has both U153 and PY81 on the envelope.
The ends of the anode plates are turned out to give the maximum cooling in the small space available. The ceramic insulating tube lining the cathode tube can be seen at the top of the image.
The stitched anode plates and the cathode connection to the top cap.
The thin glass tube envelope is 19 mm in diameter and, excluding the B9A base pins, is 71 mm tall.
References: Data-sheet & 3002. Type U153 was first introduced in 1953. See also1953 adverts.
