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ECH81

Sensibly equivalent to:
6AJ8 6C12 CV2128 X719
    
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The ECH81 triode heptode was designed in 1954 for the role of frequency changer (mixer) in superhet receivers for AM reception. The ECH81 acting as oscillator and mixer for AM and the heptode being the first IF amplifier on FM.
The two valve sections share a common cathode. The triode is to be used as the local oscillator feeding the 13 Volts 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 455 KHz would be typical for AM.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 60 mm tall.
References: Datasheet & 1040. Type ECH81 was first introduced in 1953.

 

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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