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X719

Sensibly equivalent to:
6AJ8 6C12 CV2128 ECH81
    
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The X719 from Emitron carries the Mullard ECH81 type designation as well as the fact that Emitron is a trade mark of Electrical & Musical Industries (EMI).
The X719 triode heptode was designed for the role of frequency changer (mixer) in superhet receivers, the two valves share a common cathode. The triode is to be used as the local oscillator feeding the 13 Volts peak to peak amplitude sine wave to the heptode mixer. Within the heptode, non linear operating causes the signals to interact to produce in the anode waveform the following major frequencies: signal, LO, signal + LO and signal minus LO. The anode circuit is tuned to enhance one of these signals, normally signal minus LO. For radio reception at the time an intermediate frequency of 455KHz would be typical.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 58 mm tall.
Reference: Data-sheet. Type X719 was first introduced in 1955. See also 1955 adverts.

 

Pin Connections
B9A
1
2
3
4
5
6
7
8
9
g2,g4
g1
k,g5,s
h
h
a
g1
a(t)
g1(t)

 

Absolute Maximum Operating Conditions
Triode
Vh
Ah
Va
mAa
6.3
0.3
100
13

 

Absolute Maximum Operating Conditions
Heptode
Va
Vs
Vg
mAa
mAs
ra
gm
250
250
-2
6.5
3.8
0.7M
0.775
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated February 26, 2013.
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