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 suppression of noise that would otherwise cause sync errors.
The ECH84 replaces the ECH81 for television systems. The ECH81 was never designed for more than AM broadcast receivers whereas the ECH84 is purpose designed for TV receivers.
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 suitable as a low level AM modulator.