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The Mullard 85A2 is a small, special quality voltage stabiliser. The striking voltage is 115 Volts and the maintaining voltage is 85 Volts. For a tube current variation of 1 mA to 10 mA the voltage regulation is 4 Volts.

This valve would have been used to directly stabilise the voltage for an oscillator or be employed as a voltage reference for a stabilised supply. In the latter case the tube would be operated at constant current.

In early 1955 Mullard brought out two special quality versions of this stabiliser. The new designs were designed to operate in the presence of vibration whilst maintaining a long life and were aimed at industrial and military applications. Type M8098 fitted with a B7G base and type M8142 with flying leads for direct soldering into circuit.

The interesting thing about this exhibit is the identification label. This places this valve within the BBC in 1954. This valve was also used in UK government equipment under the reference CV449.

The thin glass tube envelope is 17 mm in diameter and excluding the B7G base pins, is 46 mm long.

References: Data-sheet. Type 85A2 was first introduced in 1950. See also 1950 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.