EL 34 question

Dan,
IMHO the issue you are facing is fundamental one in that you are hearing the difference in amplifier topology - the EL34 amp is a push-pull probably configured as a pentode amp while the 300B is a single-ended (as you wrote) amp. The EL34 is a pentode tube but it can be configured as a pentode or as a triode. The pentode configuration gives more output power but at higher distortion. The triode configuration gives lower power but with lower distortion. I used to own a Cary/AES Sixpac that used EL34 in triode configuration & the sonics were really very good. (Too bad for me that I bought a 1-ohm version Apogee Scintilla that the Sixpac just could not drive!).
The push-pull amp will have more distortion (pentode config) & maybe even cross-over distortion since one/one set of tubes will be used to push & the other/other set will be used to pull. The matching of the push-pull pair is critical & it will never be perfect.
The SET amp uses just 1 300B tube to push & pull. so, by design the push pull ckts are perfectly matched - it's the same tube doing both! The distortion is (way) less.
Plus, reading other tube users' comments, it seems that the 300B has some sonic attributes that the EL34 simply does not have.
IMHO, Jjrenman was on the right path when he changed his pentode amp to a triode configuration (it is also why I chose the Sixpac as I, too, want a the pentode EL34 configured as a triode).
BTW, the 300B is a triode tube (& it sounds awesome) - there's a correlation here......

Did you get a good deal on the Fatboy tubes. Hope they from the 60,s. Sylvania or RCA.I have 3 quads NOS. Got lucky bought them years ago when not so expensive.

"Jjrenman was on the right path when he changed his pentode amp to a triode configuration"

Yes, changing my amp from pentode to triode was an improvement, easy to do and you only give up 3db of output. However IMO, changing from fixed bias to cathode bias was a bigger improvement. You give up even more output when you do this however the amp handled dynamics better! Must have something to do with how a cathode biased amp recovers from very demanding dynamic peak output. IMO, it is why SET amps seem to play and handle dynamics much better than their low wattage output would have you believe.

Ryriken- Expensive but hopefully worth the price of admission. I have heard a of a few LM owners gaining a nice improvement changing factory tubes. Very nice amp as is for the money though. I assume you like the Amperex Hollands?

Fjn04
I have 5 NOS Mullard Holland that test very good, don't use them yet, i dig those Fatboys in my VTL ST 85 amp.Come to think of it they may be Amperex but i think Mullard.