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MKT4/7

Sensibly equivalent to:
7A2 A70B AC/Pen APP4A CV1683 KT42 MP/Pen N40 P4VA Pen4VA
    
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The valve shown is an MKT4/7, ie fitted with a B7 basecap. Most MKT4/5's were fitted with B5 base caps with the screen grid connected to a side terminal.
The MKT4 shown in the photo is a late (c. 1950) specimen and has a distinct Cossor look about it. It is probably a Cossor MP/Pen re-labeled as an M-OV valve.
In single ended audio configuration would provide an adequate 2.5 Watts.
Some pre-war EMI television receivers used the MKT4/7 as a line output valve.
It was a design that was produced by several different manufacturers. Note also that MP-Pen, MPPen, MP/Pen are variants describing the same type of valve.
The classic envelope is 53 mm in diameter, and excluding the B7 base pins, is 110 mm tall.
References: Datasheet, 1043 & 1040. Type MKT4/7 was first introduced in 1937.

 

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

 

Absolute Maximum Operating Conditions
Beam Tetrode
Vh
Ah
Va
Vs
Vg
mAa
mAs
gm
Pout
D
4.0
1.0
250
225
-13.5
32
5
3
2.5W
10%
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated December14, 2012.
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