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3A/108A

Sensibly equivalent to:
CV1653
    
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The 3A/108A is a telephone repeater triode. The design dates from 1947 and it was made for replacement purposes. The 3A/108B is the same valve but fitted with a B5 base cap.
This is a low power amplifier and the anode is a bright box.
Looking into the dome. The oxide coated filament is M shaped and held by two tension springs.
The springs ate fixed to the top mica. The white of the filament coating can be seen between the grid wires.
The classic envelope is 45 mm in diameter, and excluding the American 4-pin bayonet base pins is 103 mm tall.
Reference: Datasheet. Type 3A/108A was first introduced in 1947.

 

Pin Connections
1
2
3
4
g1
f-
f+
a

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
μ
2.0
0.2
160
-1.5
-
50,000
0.6
30
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated February 14, 2013.
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