Ed,
A properly operating TX-2500 is listed at some used equipment site (I didn't bother to remember which one - sorry) for $139.00. In your case, with a defective channel, I would consider it worth approximately $25.00.
We seem to be having quite a few folks who are asking "What's my (Insert make and model here) worth?" At the risk of repeating myself, the answer is: "It's worth whatever you can get someone else to pay for it." OR, the answer is: "What's it worth to YOU?"
There are VERY few particular makes and models of "vintage" solid-state amps, preamps, tuners or receivers that command any sort of high price. Of COURSE, there are exceptions, but they are in the minority. But, *in general*, Japanese solid-state Stereo/Hi-Fi gear from the 1970's (again, with *some* exceptions) is not worth very much. NOBODY is going to retire by buying and selling this stuff. They made a LOT of it and it was generally the beginning of the "when it breaks, throw it away" era. Unless it happens to be full of tubes, or it was a VERY High-End, Limited-Edition model, it is HIGHLY unlikely that you will be able to sell it for a small fraction of its original price. If it isn't working properly, you *might* have to PAY someone to haul it away!
Don't shoot the messenger!
Sincerely,
Bill Thomas