Ah, memories from the early '70's... I remember selling and buying these - a solid sell that NEVER came back to haunt me.
Some of the special features were the “glide path” volume controls which featured dual pots for each slider so that loudness enhancement effect was continuously variable from minimal at loud volume to maximum when played softly, based on the position of the volume slider. Caution - Don't spray contact cleaner on the volume sliders though. They are specially treated and respond best to a few minutes of gentle exercise up and down to scrape the contact points clean. (with the power off, of course)
I used to have 2 of these – one I got for my folks and one was my own. My own unit was sold to a classmate when I left college, because I did not need all the equipment I had collected during my years of working at RS to pay my way through school.
The "B" version was essentially a higher power version of the original, as the "power wars" went into full swing. In the ads, even the original was rated at 140 Watts but that was an IHF rating for the max from a single driven channel, but doubled by adding the two channels together. I liked to call that "Impending Hot Failure" because you only got that much for an Instant, only in the middle of the usual frequency range, before the power supply caps were tapped out and said "Phooey, I'm done." In actuality, the 20-20k output would be about 30 - 35 W RMS per channel for early units and ramping up over time through various revisions. Still more than enough for the ported speakers that were popular until "Acoustic Suspension" sealed cabinets became all the rage.
Don't get me wrong - I loved this unit in its day, and I may even have one in storage still. I'll know in the next year or so as I rummage through my old stuff while downsizing yet again. I used my STA-120 to drive my Bose 901 series 1's but when I moved on to Quad, I added some Infinity 1001's and upgraded my power to HK Citation and Crown. My folks used their STA-120 until they had both passed away and I inherited it back. That was over 25 years of daily use with zero issues.
At this point, I would suggest you have someone check all the caps, and if you are serious about this unit, also replace some of the transistors, which are known to be a bit noisy, as well. Nice find! Enjoy!!
