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NT20

Sensibly equivalent to:
CV1208 P625 PM256 PM365
    
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The NT20 is a directly heated triode. The NT indicates a UK Navy transmitting valve. With the advent of the CV system for Government procurement the Type was renamed the CV1208. The prototypes were the P625 and the PM256.
The front to back dimension is 6 mm.
The base pins and above the pinch is the lower mica. The oxide coated filament can be seen through the hole in the mica sheet.
The top mica and filament tension springs. The filament coating has flaked off in places.
The four filament strands and the grid winding.
The classic envelope is 45 mm in diameter, and excluding the B4 base pins is 103 mm tall.
Reference: Datasheet.

 

Pin Connections
B4
1
2
3
4
a
g1
f
f

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
Vg
mAa
ra
gm
μ
6.0
0.25
250
-
55.0
2,000
3.2
6
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated April 06, 2019.
shape:classic construction:pinch type:triode age:1930.1940 base:b4 heater:6.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f
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