Like I said, 50% winding make 60VAC RMS, 1.4x that - 1volt=83V Peak. If your really have two independent center tapped windings, then you could use double diodes instead of bridges. You can either parallel them for a super ST120, or stack them for +-83V to make something like a Peavey 1.3K. I've got six or ten motor drive heatsinks, but you can probably find a maintenance man at a food plant out there that can fish them out of the dumpster for you. (Food plants kill lots of motor drives with the washdown process).
You'll need something like +- 15 for op amps, the cheapest stuff I know is wall-transformers at a $1 each in a grocery cart at Salvation Army resale shop.
Finding speakers that will take 75 volts is not hard- Say Peavey SP3 or SP7BW. Owning a hall that needs them, and moving them there is the problem. A pair of SP7's came up on craigslist here yesterday, they weigh about 150 lb and are on casters. They would not fit in my car like the SP2's did, I'd have to rent a truck. Oh, BTW, I bought a real Peavey 1.3k amp in September, inop, for $65. My winter project. I'm making 3 ST120 channels this winter to transistorize my organ, +83 is perfect for a single ended ST120. Look at this link too, the single ended fet amp
http://www.angelfire.com/ab3/mjramp/mjr8-2.html