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The 9004 is a good example of an acorn diode valve. The type designation is missing but the markings H4E remain. Acorn valves appeared in the late 1930s as more use was made of the VHF part of the spectrum and smaller inter-electrode capacitances were essential.

We have no details about this exhibit but visual inspection reveals an indirectly heated cathode and a flat plate anode with a small cylindrical bulge in the centre to house the other electrodes.

The thin glass tube envelope is 20 mm in diameter and, excluding the base pins, is 33 mm tall.

References: Data-sheet. Type 9004 was first introduced in 1943. See also 1943 adverts.

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.