Disadvantages of buying old solid state.

+2 @chayro, What balanced preamp did you purchase?

Mike

Electrolytic capacitors start drying out and need replacement. Bryson offers a 5 year warranty on used amps.

I would discuss with Mark at Reno Hi Fi ! Very reputable dealership of current and used Pass Equipment. 

Chuck

First, on balanced versus unbalanced. Whenever this option comes up, you really have to try it to see if one is better than the other with your components.
 

For instance I have Audio Research equipment. ARC recommends the use of balanced interconnects because the internal designs of both the amp and preamp are balanced. I tried both, I can’t tell the difference. This is not always true, but typically it is not a big difference if any difference can be heard (other than volume…. Which is of no consequence to your system… it will not play louder, it is just the characteristic of the interconnects). My point is, this is not a reason to swap amps… particularly to one older than ten years. It is more likely… the difference in character or age will have a bigger impact.

But if you want a new amp… great idea… focus on the amp / sound character and as you are getting close… just verify it is a balanced design. I would put this at the very end of the list of requirements.

                                              +1 on electrolytic replacement.

     It’s unfortunate, but: some of the older values and/or dimensions can be hard to locate, unless the amp manufacturer stocks them.

     With the way some amps are configured (internal build/PC board mount/etc); that can present a problem.    Especially: when looking for the larger filter caps