Originally Posted by: stahlhart... I guess that if you're really a glutton for punishment, you can measure all of the resistors to see if any have significantly changed value from aging, too... but the GU-12 is working quite well at the moment, so I'm thinking that there isn't anything to far off. At some point I'm going to go through them all, just to make sure, though. ...

Unless somethings is obviously wrong, there's probably very little to gain from replacing resistors. The originals were +/- 5% tolerance to begin with, and they would have pretty much stopped drifting 20 years ago. In other words, if it ain't broken, don't try to fix it. You could find that you lose the mojo by bringing everything back to exact design values. Or it might sound better. Given the amount of work involved, I'd be inclined to leave it alone unless it was mis-behaving.