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X719

Sensibly equivalent to:
6AJ8 6C12 CV2128 ECH81
    
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The X719 from Marconi also carries the Mullard ECH81 type designation. This in part a recognition of the market dominance of Mullard at this time. Also a way of making more customer's aware that the Marconi (M-OV) product was able to be used as a straight replacement for the Mullard product.
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 the valve is 57 mm tall excluding the B9A base pins.
References: Datasheet & 1040. Type X719 was first introduced in 1955.

 

Pin Connections
B9A
1
2
3
4
5
6
7
8
9
g2,g4
g1
k,g5,s
h
h
a
g3
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 October 12, 2016.
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