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.

 
Absolute Maximum Operating Conditions

Diode	Vh	Ah	Va	mAa
	6.3	0.15	117	5.0

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 12 June 2007 {find valves by name}