There was a series of relatively slim (2U chassis rather than 4U), upmarket audio separates put out by Technics in 1977: the ST-9030T tuner, SU-9070 preamplifier, and SE-9060 amplifier. They are two degrees of separation from the top of the line models at the time, the range went 9600>9200>90x0.
I recently acquired the tuner (more on that some other time) and have the others in my sights.
For educational purposes, the amplifier schematic for the SE-9060 is shown below. The input stage and voltage amplifier was driven from regulated 55 V supplies (Va+ Va-), while the driver stage was powered directly by the rectified DC at about 50 V (Vb+ Vb-) filtered with 18,000 uF per rail per channel.
Note that there were 9060 and 9060II as well as 9070 and 9070II models in Japan, but the export model of the preamp which sold as the 9070 was actually the 9070II
rather than the 9070
domestic version. Likewise the SE-9060 shown below (from a European...