To the folks somewhere back up in the thread: What were you all saying about guitar amplifier snobs wanting the original caps in their amps? I've always thought that 'stuffing' old caps was quite a bit nutty too.
The whole thing about the caps in guitar amps primarily has to do with the tonal qualities of the amp vs. the types of caps used in its build. It's not necessarily the old caps that give it 'the sound'. It's what type of caps give it 'the sound'. It's usually a matter of PIO (paper in oil) vs. Poly/Mylar. (I call it "IT". PIO caps have "IT" while Poly/Mylar caps do not). The sound guitarists are looking for is a combination of tone coloration, breakup/distortion and compression/sag. Power filter caps do not generally affect the tone but rather the responsiveness of the amp. Old filter caps allow a lot of sag in the power supply which lends the amp to having a natural compression on it's output. Beefing up the power supply with new and/or larger capacity filters tightens up the amp and gives it's output a more aggressive attack. Replaced filter caps in the power supply are usually not viewed as a bad thing. Sag can also be adjusted with use of different rectifier tubes. Breakup/distortion is most easily achieved and controlled with preamp tube gain and speaker cone material, design and size.
The caps that matter the most in a guitar are in the tone stack/circuit. In a vintage amp the worst possible thing you can do is change these, especially if they were relatively in spec. It's generally agreed that PIO caps have a richer harmonic quality than Mylar. I know in theory it doesn't make any sense but when you hear them side by side, there is a difference. I didn't believe it either until I tried it. Aside from the amp, the PIO caps in the tone control in the guitar have an even more dramatic effect than they do in the amp. Most guitars have the tiniest most basic of Mylar caps(some even use ceramic caps) on their tone controls. When you swap those out for a PIO cap, it completely changes the harmonic richness of the guitar's output. The tone control becomes much smoother and more responsive to change. Any PIO is good for this but the general consensus is Sprague Bumblebees, Black Beauties and Vitamin Q's are the best(hence they want the "old" caps).
SO, in the future, don't go knocking somebody about wanting old caps in their guitar amps and they won't laugh at you for being anal enough to spend countless hours stuffing new caps into old caps. Because both schools of thought are a little nutty.
