A-ha ! Thank you Sir.
I've had 2 old ST70's in my garage for a decade now. (free, courtesy of my Father-in law, who lacks storage space in NYC) I've put off restoring them because I felt I didn't fully understand how the circuits work. I realized that I don't fully understand how computers work either, but that hasn't stopped me from building over 20 in the last decade. I'm not surprised that my 1st question reflects my lack of understanding regarding electronics ! I'll try to finish this amp on my own, but you may get some more newbie questions from me.