Note
QST, Apr 1971, p. 1. (SR-400A)
QST, Jan 1972, p. 1.
QST, Apr 1974, inside front cover.
QST, Jul 1974, p. 161. (on sale)
The most significant improvement in the SR-400A “Cyclone III” transceiver over the SR-400 was increased power. Input power to the 6DK6 finals was 550 watts on SSB and 350 watts on CW. The transceiver covered 80–10 meters and required an external power supply, PS-500A.
Other improvements included an power-amplifier-tube balancing circuit that eliminated the need for matched tubes, a new built-in 100/25 kHz crystal calibrator, and calibrated RIT.
When used with the HA-20 remote VFO, permits listening to two frequencies simultaneously. This isn't a new feature. The SR-400 could do this as well.
An expanded VSWR meter with remote bridge connection allows the continuous checking of antennas performance.
Optional fixed station blower kit.
References
Review (SR-400): QST. Oct 1968, p. 49.
Brief description. Electronics World, Sep 1969, p. 80.