From the manufacturer:
"SE-A1 Stereo Power Amplifier
By developing Class A+ operation that provided amazing 350 W + 350 W output power, Technics aimed to achieve the highest level of power amp performance with the SE-A1. Theoretically, Class A operation does not generate switching distortion or crossover distortion. On the other hand, it is low in efficiency, so it is difficult to produce a high-power Class A amp. The Class A+ operation employed in the SE-A1 was similar to the Class A operation, which constantly requires electric current, but with floating ground potential. This system supplied high voltage from a separate power supply amp as needed in sync with the audio signal amplitude. This achieved high output power without using a forced air cooling fan, thus enabling a compact housing. The SE-A1 was a full-fledged DC amp, and boasted excellent waveform transmission performance. The active thermal servo circuit suppressed DC drift. The power supply section featured a dual monaural structure with four power supply units per channel for a total of eight power supply units. The peak meter was a quick-response type. The SE-A1 and SU-A2 were made-to-order, and only one unit was produced per day. The SE-A1 developed in pursuit of the highest possible performance had a considerable impact on the industry.
SU-A2 Stereo Control Amplifier
Using Class A operation in all stages, the SU-A2 was completely free of switching and crossover distortion, and realised low distortion and a high S/N ratio. Featuring the DC amp structure, the SU-A2 used no capacitors and achieved faithful waveform transmission. From the Phono MM input to the output terminals, the rated distortion factor was 0.003% in the range of 20 Hz to 20 kHz (at 1-V output). The SU-A2 was provided with a low-noise dual FET for MM and a newly developed low-noise transistor for the MC preamp. Use of the active thermal servo amp minimised DC drift. Despite the multi-functionality, the simplified wiring and switches in each section offered minimal crosstalk. The universal frequency equaliser was configured with four elements in each channel for a total of eight elements. The SU-A2 was highlighted as the most advanced, top-level control amp of the day."