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The CV5277 is a high speed counting tube and was developed about 1959. Commercially this is a Mullard ET51. These counter tubes were known as Decade Selector Tubes, Beam-X Tubes and Trochotrons. The latter being derived from the mathematical shape of the beam. A trochodial shape being defined as the locus of a point on a circle that is rotated along a line. In simple terms it is a spiky spiral.

By using a beam of electrons that were controlled by a powerful static magnetic field and dynamic electric fields, speeds of 1 MHz or more were possible. This is an order of magnitude greater than the Dekatron type counters that used ionised neon gas.

The base pins are positioned in two rings. The outer with 17 pins and the inner with 9. The central glass valve is surrounded by a powerful ring magnet cemented into place. The plastic base ring and top dome are cosmetic.

The target voltage is 200 Volts and the series resistor is 18,000 Ohms. The cathode current is a maximum or 6.5 mA with 5.5 mA for the active target. The spade voltage is 100 Volts and the spade resistor is 0.1 MΩ. The cathode is heated by an indirect heater running at 6.3 Volts and 0.3 Amps.

The correct operation depended on the uniformity of the magnetic field. These tubes had to be a minimum of 100 mm apart. The guidance advises that they should not be struck or allowed to come into contact with other magnetic material.

The envelope is 42 mm in diameter, and excluding the B26A base pins is 75 mm tall.

References: Data-sheet, Advert & ³⁰⁰². Type CV5277 was first introduced in 1960. See also 1960 adverts.

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.