The ECH81 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 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.

From the side, through the screen, can be seen two sizes of electrodes. Under a glass the lower section can be seen to contain several wire grid spirals. Above the main assembly the cathode continues and a single grid can be seen. This suggests the triode is mounted above the mixer on the common cathode tube.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 55 mm tall.

 
Pin Connections

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

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	mAa
	6.3	0.3	100	13

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 datasheet

This exhibit was last updated on 08 June 2007 {find valves by name}