A quick clip comparing the '68 Princeton Reverb to the '65 Princeton Reverb. An SM57 was used on both amps in the exact same spot. I used a Fender Custom Shop 1962 Masterbuilt Strat with Fat 50's pickups. Sorry about the lame frame-up but I wasn't planning on turning it into a Youtube vid until I figured that it could be useful for y'all!
It's rather obvious that the '68 has a bigger sound, mostly thanks to the Celestion Speaker. The '65 sounds thin by comparison. However when trying to get a guitar to sit in the mix, especially a Fender, sometimes that thinner sound is easier to place.
Hopefully this clip helps you hear the differences between these two incredible little amps.