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The 1A3 is a signal diode and features a 1.4 Volt indirectly heated cathode. Normally dry battery valves are directly heated. Such a valve would find applications where the cathode is not taken to ground or where the filaments of other valves are run in series from a higher voltage supply. Two such valves could be used in a discriminator in an FM radio in the 1950s.

The heater wire is a single thread running vertically through the anode cavity.

Seen from the side the anode can be seen as two fins with a central cylindrical cavity for the cathode.

The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 45 mm tall.

References: Datasheet & ³⁰⁰² Type 1A3 was first introduced in 1943.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.