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12K8GT

Sensibly equivalent to:
CV3927 X71M X76M
See also:
The 'Magic Three' Valves
    
Extras ▼

 

The 12K8GT was purpose designed as a frequency changer valve for use in the broadcast bands. It has a common cathode and is unusual within our collection in that the triode and hexode control grids are internally connected.
The local oscillator would produce 7.5 Volts peak to peak signal from the triode section.
The input signal would be coupled to the frequency changer via the top cap connection to grid 3 thus maximising oscillator and signal circuits. The micas are shaped to fit the envelope and hold the electrodes firmly. The notched grid supports can be seen.
Seen from the top of the base skirt the image reveals the pinch and connections to the main assembly. The heater wire is welded to the supports and as it rises to the cathode the insulating coating is visible as a thickening of the wire.
See also 6K8.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 74 mm tall.
References: Datasheet, 1040 & 1043.

 

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

 

Absolute Maximum Operating Conditions
Hexode
Vh
Ah
Va
Vs
Vg
mAa
mAs
ra
gm
12.6
0.15
250
100
-3
2.5
6
0.6M
0.36

 

Absolute Maximum Operating Conditions
Triode
Va
mAa
100
3.8
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated January 28, 2013.
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