I know this is a little off target ,but in my experience as long as you take care of the amp and don't routinely flog it, it will last a very long time with very little degradation. The beauty of amps is that they are always analog in and out so they just don't go obsolete. Unless damaged in some way they will last forever. I have several solid state amps that I purchased back in the 70s which still sound great today. The only difference is that the older amps outweigh the newer models in the pounds per watt category.