You're all pretty much correct. The way I hear it...the Weber is a little "thicker" than the JCM 800, which is tighter and punchier than the Weber, and the vintage JMP somehow has all of it combined. And though the master volume was on 4 for all three amps they were loud as fucking hell. Four is around the first tipping point where the power section starts to kick in and it's already way louder than you could use at any normal bar/club gig.
Some interesting (to me) tidbits that sort of explain how these amps can make different sounds when set the same....
1) Pot tapers and human imperfections. Can't do anything about that. Maybe I had the gain on 8 on one amp, 8.3 on another, 7.7 on another. I don't know, I just put it around 8. Maybe they were exactly the same and the gain/volume/tone pots are using their built-in 10% tolerance? I don't know, nor do I care. That's life. Even on their best day these types of amps are very touchy on the volume control. They go from not enough to blow your face off real easily. You can also tell in the clips that the JMP is louder at "4" than the other two. I chalk that up to pot taper.
2) Tubes. The weber has brand new chinese tubes. The JCM has well-worn in JJs. The JMP has it's actual vintage preamp tubes still in it. Does it matter? Maybe a little. I'm not a huge believer in tubes making a lot of difference if they're good. Swapping good tubes for good tubes is usually diminishing returns cork-sniffery. I do know for a fact that chinese tubes do tend to be a little "hotter" though. That could explain some of the gain and thickness of the Weber. They're also microphonic because they're chinese. I had to swap the Weber's three12AX7s around several times to find the best combination. Better tubes in the Weber might yield much different results.
3) Filtering and voltages. In my mind this is where things really happen. The Weber is configured like a 50w Marshall and/or late-80s 100w. It has less filtering and higher preamp voltages than a typical 2203. It has exactly the type of filtering and voltages you'd find in a 50w model. Why'd they do this? No idea. But it makes for a slightly looser low end and a more aggressive bite overall. It sounds like a modern-era 100w JCM 800. The real JCM and JMP have twice the filtering that the Weber kit has and you can hear and feel it from the amps. The low end is super tight and controlled and there's a lot of headroom from both the JCM and JMP. But where the JMP runs away is it has insane voltages like the Weber! So it has all of it. Mucho filtering and crazy high voltages. So it gets controlled aggression...which is a good thing IMO.
4) Components and time. The Weber has brand new no-name kit components. They all measure perfectly fine and are working perfectly fine. The JCM and JMP have settled into what they are and have sought-after vintage caps and resistors all over them. Do they make a sound? I think they do a little bit. There is a "smoothing" kind of effect with worn in parts and/or period-correct new parts. Like a carbon vs metal film resistor. There is a difference depending on where you use them. I expect that the Weber will just get better as it breaks-in...if it doesn't just break.
BTW
@WhiskeyJack that JMP is the Canadian Fawn.
