some of the guys ive seen dont even have to look at the replacement caps, they just listen to the hum frequency, im not that much into vintage amps, if it sounds good then it is good, ive been on VOX forums and those guys are real anoraks, they even discusss the types of alloy metal used to make the serial number ID plates on the amp case.
I remember a recent good thread, every year in sunny california there is an event called VOXfest, and they all get together and swap vintage 20amp 3 core OFC cable with the 70% plastic 25% bakalite 5% BS cable, and all stand around drooling over unused original condition Mallard EL84 valves, you know the sort of thing. Well one particular year they had a broad representation of the VOX amp over the years, and they set these amps up behind a thin curtain, amongst others there was an original 60’s VOX AC30 JMI (at this point we have to get on our knees and pay homage) then they had a 70’s AC30 which was basicaly a tranistor amp that looked like a vox, and was made by Rose Morris, then we had a brand new out of the box Korg/VOX AC30 with blue speakers, and they had amongst others a heavily modified AC30 owned and modded by one of the west coast VOX guru’s, some top members of ‘The Club’ went along and listened to these amps one at a time while someone played through them from behind the curtain, the members marked them and gave in the scores, top of the list came the ‘Modded’ amp, which was expected, but in 2nd place above all the 60’s JMI models was a new out of the box (complete with printed circuit board) Korg AC30, this is the amp that was considered rubbish by the members, there was a few red faces that year, and as an offer of explanation they said it was because the new blue alnico speakers were that much ‘fresher’ .
Sometimes people take this ‘vintage’ thing too far, they want to hear differences in tone becuase they have conditioned themselves to believe that there is a difference, all very strange, its like i always say, if it sounds good to you, then it is good…… but only by your ears!