Hi Michael ... so ... I guess my interest in Gibson amps is hanging out pretty far..... :wink: ... The closest Gibson match to a Princeton Reverb, the
AA1164 model, is a Gibson GA19RVT
circuit here. both with 4 preamp tubes, trem and reverb, twin 6V6s, GZ34 rectifier (PR) and 5Y3 rectifier (GA19RVT). Both have one preamp tube dedicated to reverb drive/recovery and another 1/2 to tremolo.
On
this webpage, a guy tries the match-'em-up exercise which is as much schematic-driven as it is tone-driven. For example, he equates the PR to any of a Gibson 20RVT(Minuteman: twin 6BQ5s), Gibson GA25RVT (Hawk: twin 6BQ5s), or a Gibson GA35RVT (Lancer; twin 7591s). As far as this gentleman's observations go, I'll leave it to you; you have/had both a GA5 w/ a 6V6 and one with a 6BQ5/EL84 ... so, if the two tubes sounded the same to you, then you might give this guy's remarks some weight. I don't think they sound alike so it's hard for me to get on board with his comparisons.
Our new BBer DgP just bought a GA19RVT discussed
Here. The thread also contains a link to an eBay auction where a VGC GA19RVT recently went for big money (DgP's wasn't inexpensive!). The PR runs its 6V6s at 410V, the GA19RVT closer to 300V, they have different phase inverter designs, and the PR has a slightly larger OT all of which suggests the PR will be cleaner at higher volumes but will lack the Gibson's timbre-rich, highly compressed brown-sound.
Gibson got its GA19RVT tweed model to market sooner than Fender produced the Princeton Reverb. Shortly afterwards, Gibson morphed the tweed model to the 'Crest' version; a very-good selling amp; early models with 6V6s, later ones with 7591s. Can't say for sure but believe the 'Crest' model to produce a cleaner tone than the tweed version ... Gibson continued with smallish output transformers under its cost engineering mantra: "We never met a cost we couldn't avoid". Hope this helps. John