This MH4 has the suffix /K, probably to denote the Catkin assembly as opposed to the conventional glass envelope type. As can be seen from the picture, this is a strange valve. The Catkin process was introduced in 1931 by MOV, the valves were very successful but the cost of manufacture lead this production method to be short lived. The Cooled Anode Transmitting (CAT) valves, that the Catkin process was derived from, remained highly successful.

The top envelope is enamelled copper sealed to glass, no internal structure can be seen. The large wide base holds the pinch and a rubber sealing ring. The metal base tube is 25 mm in diameter. The heater rating at 4 Volts and 1 Amp was the UK standard until the American's introduced the 6.3 Volt heater in the mid 1930s.

The thin metal tube envelope is 12 mm in diameter and, excluding the B5 base pins, is 95 mm tall.

 
Pin Connections

B5	1	2	3	4	5
	a	g	h	h	k

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	4.0	1.0	250	-4	5.0	11,100	3.6

Thanks to Frank Philipse for supplying the above datasheet

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This exhibit was last updated on 02 December 2007 {find valves by name}