For your info Dave, Optionica was a trade name, a trade mark, wholly owned and produced by Sharp of Japan.
It most certainly is NOT a no-name product. The Optionica name was started in Sharp's attempt to start up a trade mark with a higher profile than Sharp usually has, what with needle to locomotive portfolio. Much like Technics was started up by Matsushita, who also own the Panasonic brand name, or Toyota starting up Lexus, etc.
In those days, circa mid-70, when somebody did that, they had to be quite a bit better than the rest if they wanted to make it in a crowded market. So, let's just say you were a little lucky and unwittingly bought what I expect to be a very fair product. Not Levinson, but not your run-off-the-mill el cheapo stuff either.
Cheers,
DVV