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The KY80 is the Mullard designation for the U26. The fact that the Mullard designation does not take pride of place on the envelope shows that they were not the original designers.

The U26/KY80 is a purpose designed EHT rectifier for television picture tube supplies. It would be fed from an EHT overwind on the line output transformer and not a sine wave input. The valve is specified for a peak inverse voltage of 23,500 Volts. With a spike voltage input this suggests 17 - 18 kV for the picture tube. Normal 15 - 17 inch black and white. The reservoir capacitor would be made from the coatings on the inside and outside of the picture tube and needs to be less than 0.001 µF.

The heater is designed to be driven from the line output transformer and not connected as part of the normal heater chain.

The valve features a bell shaped anode cylinder with a wide separation to the cathode as befits such a high voltage device.

The thin glass tube envelope is 19 mm in diameter and excluding the B9A base pins, is 65 mm in length.

References: Data-sheet & ¹⁰⁴⁰.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.