The ECH84 is a low voltage triode heptode. The ECH84 was specifically designed for operation as a sync separator in negative-modulation television receivers, the dual control feature of the heptode allowing the supression of noise that would otherwise cause sync errors.
The triode heptode could be also used as a frequency changer for medium and long wave radio receivers. The heptode has a straight characteristic that makes it suited as AM modulator.