Note
QST, Sep 1971, p. 128.
QST, Jan 1972, p. 158.
QST, Oct 1972, p. 141.
QST, Jul 1973, p. 175.
QST, Jan 1974, p. 175.
The HAL 1550 keyer used TTL ICs. Its keying transistor worked with either cathode or grid block transmitters. An optional ID PROM was available. $90.00 (with ID).