Lmao you must be referring to Aussie Brad!
Man, thats a deep philosophical question for certain— and no two dudes agree. In my opinion, discreet components make more of a difference in single channel amps or on clean channels, where there aren’t tons of snubber caps lopping off high end from the preamp. Still an amp is the sum if its parts, so I’d say that for my money the most sensitive cap placements are in decoupling positions.
Panasonic ECQ series are AMAZING in all positions. The little, magical, Blue Molded Ajax caps in vintage fenders are truly special. Truly. The ECQs sound JUST LIKE THEM. Additionally, they have very compact form factor! Look on eBay - you will often find sellers getting rid of lots of these for a great price. I have a biz agreement with a major parts supplier in Arizona and usually get parts for a nice discount, but still peruse the ‘bay for special deals. I gobble up all the common values I can find (.001, .003, .01, .02, .047, etc). My customers love love love them. And they are very reliable. When I sometimes have to deliver bad news about their prized pi caps, their anxiety is vanquished once they play the amp.
With respect to resistors, I like carbon film for most positions, except for plate loads, where I hugely favor carbon comps in the 1/2-1w range; there‘s a non-linearity in the way they respond to operating conditions that’s adds a little something. It’s impossible to describe, but there’s something missing when they aren’t there. When I’m doing vintage restos, I never sub in any other type for the preamp plate supply. That’s critical duty.
But - all this is just one guy’s worthless opinion.
@ forgotten gear restorations