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The PM2HL battery triode was designed as a small signal amplifier. The valve is of medium impedance.

This example has a clear envelope thus revealing the electrodes.

The box anode has a W shaped filament allowing for four emitting surfaces. Filament tension is maintained by coil springs attached to the top mica. The fact that the envelope is clear and a top mica is used indicates a late production with an spray coated oxide filament rather than the earlier Azide process filament.

The balloon envelope is 41 mm in diameter and, excluding the B4 base pins, is 86 mm tall.

References: Data-sheet & ¹⁰⁴³. Type PM2HL was first introduced in 1938. See also 1938 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Andy Cowley for supplying the above PDF datasheet.