Honestly if I were an owner right now, a solid 60 Watts x2 would be OK with me, even at THD a point or 2 above 1%. I’d certainly be disappointed at being sold misleading/erroneous specifications, but that would be "close enough" - 60 versus 75 is still usefully powerful. 17 - 20 is another story. Hopefully we'll get more clarity soon.
I know W4S cited the PT, but I’ll be really surprised if those OPT’s push out 60 Watts x2 as recognizable music.
Anyways, my audio tech & now dealer has been Gordon Waters here in Marietta GA for many years. He’s designed speakers and restored countless vintage tube amps (including a couple of mine). I trust him implicitly. On Audiokarma he posted the following interesting analysis about the Carver 275 schematic (which to Carver’s credit was included in the manual) - no comment on the transformers, just the circuit:
I was just having a conversation with some really astute techs about the Carver 275 amp, regarding a feature I just noticed, in the schematic:
Look at resistor R53 and R44, connected to the negative speaker lead. That’s basically the same type circuit as the original Fisher 55A "Z-Matic" output-impedance adjusting circuit, just without the adjustability that Fisher provided (including the ability to turn it off, in the Fisher!). Here, it’s set to a fixed level of current feedback, reducing the damping factor. This will act to "color" the bass of most speakers- in a not-so-predictable way (each speaker has different impedance characteristics, which will interact with the network in different ways). This is ostensibly the "listening to the speaker in the room" thing that Carver was talking about, I would think. It’s funny, though, that it’s something that most experienced techs recommend REMOVING from the Fisher amps, since it’s rarely needed (unless you have very early speakers, designed for use with for amps with very low damping factors, such as 1950s JBLs, Altecs and such), and it’s rarely beneficial...
Also, more than one tech mentioned that they were struck by the myriad compensation networks needed for stability and response modification in this amp. Low-frequency shelving on the input (though switchable), HF frequency response limiting on the output of the first gain stage, LF shelving between the phase inverter and the output tubes, HF snubbing/shelving on the primaries of the output transformers, a Zobel on the output, AND a two-stage shelving network in the feedback loop itself, as well as the "output impedance modification" circuit described above. It’s rare for ANY amp to need THAT MANY different networks. Maybe two or three, tops- for example, the Eico ST70 "Hot Rod" uses three (plate-to-grid HF compensation on the phase inverter, HF snubbing/shelving on the OPT primary, and a Zobel)- but almost never SEVEN different response-modifying networks in one amp. I wonder what square wave response looks like, under normal operation, and also with each of those networks disconnected one at a time, to see exactly what each one of them is doing...
Mind you, having all those networks doesn’t necessarily mean the amp would perform badly or sound bad- but with each network added, there’s always the chance of "throwing away the baby with the bath water", in terms of sound. Every compensation network represents a compromise of some sort...
Regards,
Gordon.
