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UCH21

 
    
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The UCH21 is an early example of all glass construction. This triode heptode frequency changer was designed to operate on a heater chain across the mains supply, and the anode voltage is correspondingly low to take account of the low HT voltage present in universal sets.
The reason why there is no cathode/g5/s pin is that the metal spigot is used for this purpose. This meant that the metal skirt operated at cathode potential, not chassis potential, creating insulation problems unless a suitably-insulated base socket was used.
The wide glass tube envelope is 27.5 mm in diameter, and excluding the B8B base pins, is 60 mm tall. The skirt has a diameter of 31.5 mm.
References: Datasheet & 3002. Type UCH21 was first introduced in 1941.

 

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

 

Absolute Maximum Operating Conditions
Heptode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
20.0
0.1
200
100
-2
3.5
6.5
1M
0.75

 

Absolute Maximum Operating Conditions
Triode
Va
mAa
120
4.1
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated February 07, 2013.
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