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VT-221

Sensibly equivalent to:
3Q5GT
    
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The VT-221 (3Q5GT) is a dry battery audio output pentode with an output of, typically, a quarter of a Watt. The filament has a centre tap so that it can be used with 1.4 Volts or 2.8 Volts, i.e. one or two dry cells.
The VT- prefix denotes a procurement code of the USA Government. The majority of the valves have a direct commercial equivalence. In the UK the Government specification could depart from the commercial prototype.
The etched Type designation appears within an octagonal border - usually associated with RCA.
The bright anode with the twin filament tensioning springs seen at the top.
The original plain cardboard carton showing that this was made for the US military during WWII.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 62 mm tall.
References: Data-sheet, 1040, 1043 & 3002.

 

Pin Connections
IO
1
2
3
4
5
6
7
8
nc
f+
a
g2
g1
nc
f-
ftap

 

Absolute Maximum Operating Conditions
Pentode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
1.4
0.1
110
110
-4.5
9.5
1.3
90,000
2.2
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated January 09, 2022.
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