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MPT4

Sensibly equivalent to:
7A2 MP/Pen Pen4VA
    
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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 M-OV 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.
This exhibit is in very good condition with no corrosion on the anode connection band around the black painted copper anode.
The Osram Catkin label.
The thin metal tube envelope is 18 mm in diameter, and excluding the B7 base pins, is 102 mm tall.
References: Datasheet. private communication & 1043. Type MPT4 was first introduced in 1931.

 

Pin Connections
B7
1
2
3
4
5
6
7
-
g1
g2
h
h
k,g3
a

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
Pout
4.0
1.0
250
250
-9.0
32
6.0
40k
3.0
3.2
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated May 13, 2016.
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