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5B/257M

Sensibly equivalent to:
CV2220
See also:
Beam Tetrodes and the 807 - STC 5B/254M, 5B/255M, 5B/257/M & 5B/258M Advert - STC 5B/254M, 5B/255M, 5B/257/M & 5B/258M Advert
    
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The 5B/257M beam tetrode was designed for transmitter use in the HF and low VHF parts of the spectrum. The design has the same rating as the 807.
In addition to RF power, the valves were designated for service as audio power amplifiers. Here the valve was to operate in class AB1 and a pair would deliver 15 Watts at 3% total distortion.
The two anode plates are joined along the flange in the centre of the heat producing region opposite the cathode. The locating pip on the base is needed as the pins are equi-spaced around a circle. The valve is also marked as a CV2220.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 76 mm tall.
References: data-sheet Type 5B/257M was first introduced in 1957. See also 1957 adverts.

 

Pin Connections
B8B
1
2
3
4
5
6
7
8
h
a
g2
k,bp
g1
g1
k,bp
h

 

Absolute Maximum Operating Conditions
Beam Tetrode
Vh
Ah
Va
Vs
Vg
mAa
mAs
mAg
Pdriv
Pout
Pdiss
freq
12.0
0.47
600
250
-45
100
8
4
0.3W
40W
25W
60
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated January 07, 2026.
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