The MPT4 is a audio output pentode Catkin valve. One of the curious ironies of the MPT4 saga is that the catkin version of 1934, although a 'blind alley', was technically very superior to the glass version MPT4. Comparison of the two photos makes it quite clear that the large anode used in the glass version could not possibly be used in the catkin version.

The two versions are, in fact, entirely different designs. The compact catkin version was possible because the external anode was directly air cooled and did not reflect excessive heat back to the cathode-grid region of the valve.

It took MOV about five years to learn how to make large glass power pentodes with grid structures which did not emit electrons, or buckle, due to overheating.

The MPT4 was designed in 1933 as an audio output pentode for all-mains broadcast radio receivers. We have the five pin B5 based MPT4 as well as this version employing the then (1933) new B7 base.

This valve requires an anode load of 9k Ohms and the catkin version of the MPT4 produces greater output than the Glass versions.

The thin metal tube envelope is 17 mm in diameter, and excluding the B7 base pins, is 102 mm tall. The base is 27 mm in diameter with a maximum diameter of 37 mm.

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout
	4.0	1.0	250	250	-13.0	32	-	-	3.0	3.2

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}