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ECH21

Sensibly equivalent to:
X143
    
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The ECH21 is an early all glass triode heptode frequency changer for radio and the design dates to the late 1940's.
The B8B base has short equi-spaced pins and a metal spigot for alignment, to cover the envelope seal and act as pin 9 for the cathode, g5 and the internal screen.
The oscillator triode was designed to produce 14 Volts peak to peak feed for the mixer section. The heptode portion is described by Mullard as suitable for AVC (AGC).
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 61 mm tall.
References: Datasheet & 1040. Type ECH21 was first introduced in 1941.

 

Pin Connections
B8B
1
2
3
4
5
6
7
8
h
a
a(t)
g1(t)
g2,g4
g1
g3
h

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
mAa
6.3
0.33
160
4.5

 

Absolute Maximum Operating Conditions
Hexode
Va
Vs
Vg
mAa
mAs
ra
gm
250
100
-2
3.0
6.2
1.4M
0.75
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated March 03, 2013.
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