The EF37 high impedance screened pentode was designed for intermediate frequency amplifier use. The high anode AC resistance suggests the use of high Q tuned circuits.

The data sheets also give parameters for use as a triode.

The first computer, Colossus, built for code breaking during WW2 made great use of these valves.

Although the original computers were destroyed after the war a rebuild has taken place at Bletchley Park. The red valves seen on the racks are the commercial EF37As, introduced after WW2 and ultimately famous for application as low noise AF voltage amplifiers. The original Colossus was built by GPO engineers who must have chosen this valve in part for its low power heater.

The classic envelope is 29 mm in diameter and, excluding the IO base pins, is 85 mm tall.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	g2	g3	nc	h	k

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.2	250	100	-2	3	0.8	2.5M	1.8

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 04 June 2007 {find valves by name}