Hi, I build pp45 amps, I’m not here to sell them, but have a few comments that I hope will be helpful.
first I would say that the power difference between 2a3 and 45 designs is a paper thing mostly, they tend to sound close-to equally powerful (or weedy depending on your speakers and tastes). They do sound subtly different but it’s more about the execution than the tubes per se.
next is the magnetics. I use the best vintage Japanese magnetics i can find, along with USA UTC parts when I can find them. Recently I made a pair and the only difference was utc vs hashimoto driver/interstage transformers, and they do not sound the same. I believe that the loading of the interstage secondary is a critical design point often glossed-over in schematics. The loading network needs a lot of design and measurement to get right.
i use exclusively Sowter 1475 phase splitter transformers and fully balanced from there on through the driver and power stages. However, sorry to have to admit this to any zealous tube-only folk among y’all, I use a transistor discrete opamp (did he just say opamp?) to drive the single ended Sowter primary (sonic imagery or sound skulptor). There is no global feedback.
of course I would say this, but these designs based on 1930’s schematics, 1940’s valves and 1960’s magnetics sound pretty damn amazing and have great clarity and sound-stage.
there is something about pp that is overlooked: the output and interstage transformers fall in and out of magnetisation at every zero-crossing of the signal (at every polarity change). That is where the transformer is at it’s least linear transfer function. Se amplifiers are different: the opt never falls out of magnetisation, never polarity reverses and always operates in its most linear region. I am convinced this is a major reason they sound different, and some would say better, than pp types using the same tubes and supporting electronics, harmonic odd/even signature aside.
last comment about bass: this is tricky to comment on. Valve amps have feeble damping factors compared to SS, but is that a good or bad thing? It’s hard to give a definitive answer, and it’s more about the speakers and the room as to whether the ‘sloppy’ bass of valves sounds better than the ‘tight‘ Bass of SS, it can go either way, so keep minds open on that… my opinion is the low damping from tube amps works pretty well with closed box speakers, but that high damping factor is necessary to control reflex port behaviour. Not sure about dipoles though.
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