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VMS4B

Sensibly equivalent to:
AC/SGVM AS4125 CV1165 MVSPen VP4
See also:
M-OV's Screened Grid Valves
    
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Type VMS4B typifies the swansong of the screen-grid receiving valve with anode top cap. It is an improved, vari-mu RF/IF tetrode intended for domestic superhet receivers but it represents the final milestone on the road which started (barely 10 years earlier) with the Type S625.
From this point on the screen-grid type was superseded by kinkless tetrode or pentode types based on American prototypes and with grid top caps.
The main advantage of the pentode or kinkless tetrode in comparison with the simpler screen-grid type was the much larger undistorted output signal handling capacity, not limited by the characteristic screen-grid kink.
This meant that kinkless valves could easily handle IF signal levels of 40 V or more without objectionable inter-modulation distortion. An IF signal level of 40 V may sound excessive but it can be needed if, say, -40 V of AGC bias has to be generated in the detector stage in order to suppress an over-loud local transmitter.
The number of equivalents suggests that this was a popular valve in its day.
Interestingly this envelope shape is the same as the Mazda AC/SGVM equivalent and not same as the later VMS4B from M-OV. It looks as if M-OV were tooling up for the KT valves and buying-in re-branded Mazda valves for the last supplies of the older SG valve.
The reverse of the metalised envelope carries a printed Osram name.
Few structural details are visible from the top and none from the base.
The classic envelope is 39 mm in diameter and, excluding the B5 base pins, is 106 mm tall.
References: Datasheet & 1005 Type VMS4B was first introduced in 1933.

 

Pin Connections
B5
1
2
3
4
5
tc
g2
g1
h
h
k
a

 

Absolute Maximum Operating Conditions
Tetrode
Vh
Ah
Va
Vs
Vg
mAa
mAs
gm
4.0
1.0
200
80
0
8.0
1.5
2.9
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated March 07, 2015.
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