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VR91A

Sensibly equivalent to:
EF50
    
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The ubiquitous red valve had a pre-CV RAF code of VR91. This exhibit is clearly a variant with the A suffix.
This amplifier pentode was a general workhorse. It was extensively used in radio and radar during WWII. This example was made in America but carries the pre-1941 VR designation of an RAF receiving valve.
The USA makers name appears on the envelope. It was normal for service valves to be left with just the type designation.
The Air Ministry logo.
The short hard pins of the B9G base and the central spigot to locate the pins correctly in the holder. The evacuation seal of this all glass valve is protected by the spigot.
The wide glass tube envelope is 33 mm in diameter, and excluding the B9G base pins is 60  mm tall.
References: Datasheet & 1040.

 

Pin Connections
B9G
1
2
3
4
5
6
7
8
9
h
g2
a
g3
s
k
g1
s
h

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
6.3
0.3
250
250
-2
10
3
1.0M
6.5
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated December06, 2012.
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