I've never put EL34s in my Recto, but I'd say your description will be accurate.

I have a Randall RT2/50 stereo power amp with 6L6GCs on one side and EL34s on the other and I can instantly A/B switch between the two tube types. Your description is what I hear. The more the volume goes up, the more apparent differences are.

I never tried EL34's when I had my Single Recto, but I've heard that the clean tone suffers quite a bit with EL34's. Curious to see what your thoughts are.

OK, here is my review after installing the EL34's.

GREEN Clean channel Normal is definitely suffering. If you need a liquid clear clean channel with a lot of headroom than EL34's are THE WRONG CHOICE. Especially for a 50w single rectifier. The clean channel went from stellar to Marshall JCM800 which I guess isn't that bad. I don't use the clean channel much anyway.

GREEN Clean channel Pushed is much better. Its pretty much straight up rock. Great for low gain crunch rock.

RED Channel Vintage (I don't use the raw setting). Very clear, very articulate. It sounds to me a little like a straight up JCM800 but with more bottom end.
RED Channel Modern. This is the setting I use 99% of the time. The sound has more punch, more mids, clearer more open highs. Bottom end sounds pretty much the same as the 6L6's. It has a lot of punch, thump and attack. I no longer notice some annoying overtones that the 6L6's produced. I also think that this sound will definitely cut through the mix easier. The best way to describe it is it sounds like a high gain Marshall amp with an EQ (or a sonic maximize) in the loop.
Reminds me a little of my old Soldano SLO100.
Bottom line. If you are into modern metal, death metal, scream or whatever they call the new cookie monster stuff.. and you detune and rarely play guitar solo's stick with the 6L6's. They have that modern new metal scooped compressed rip your heart out tone. If you want a tight thumping bottom and you want to be heard live or you are a lead player who actually plays guitar solo's go with the EL34's. They have more mids and highs and sound more open.

While you are it, try a set of 5881's in there. Not sure what it will do for a Rectifier, but it totally changed My Fireball in an amazing way. The Fireball has exceptional tone (for me), but I had that "getting lost in the mix" problem you hear a lot of Fireball owners complain about. I put in a set of Tung Sol 5881's and I haven't looked back since. The cleans are sparkling and gave the gain channel a ton of mid punch. If you do try them, I would stick with Mesa tubes and leave it on the 6L6 setting. Just a thought.

This amp isn't going to be around much longer. I have really bad GAS for a plexi. Reissue, clone, 50w, 100w... as long as it has an effects loop... I'm sold. Even with the EL34's in it.. it will always be a metal amp. I think alot of it might have to do with the cab too. I am running it through a 4 x 12 5150 bottom cab. That cab thumps like an oversized Mesa. I think the cab for me would be the one that you use to own with the X pattern in it. Half open, half closed. The Mesa Halfback.

The Plexi is a great amp but they are very loud! Almost impractical for live use in small and medium sized venues, heck even in some big ones too You'll likely end up having to consider attenuators or master volume mods. Have you been looking at any particular Plexis/Clones or waiting for a good score on one when it pops up for sale?

Interesting. Your findings regarding the EL34s are consistent with how I run my Road King II. EL34s for the leads and 6L6s for the rhythm. I usually run channel 3 in Vintage mode with 6L6s and channel 4 in Modern mode with EL34s.

That's the advantage of the Roadking. On the Single Recto series 2 its EITHER 6L6 or EL34's. I would like to run both and be able to switch them for rhythm and solo. That would be perfect.

Yeah, it's the same with the Mark V. The power section with both EL34s and 6L6s is one of those things that when you first read about it you think "who needs that", but once you try it and understand it, it's actually quite useful. Channel 1 and 2 change character quite a bit when you change the power section. Tweed mode with 6L6s is quite nice for old school Fender distortion, as is the Brit mode with EL34s, although it could have benefited from more gain IMO.

Yep... makes perfect sonic sense to me.

Update. I still have the Single Rectifier. I put the 6L6's back in for one reason. The clean channel. The 50w Rectifier simply doesn't have enough headroom to handle EL34's and have a decent clean channel. If I didn't need one... I would leave the EL34's in it but I do.

The 6L6's are whats meant to be in a Single Rectifier if you are a hard rock/metal player. EL34's literally make the green (clean) channel useless when the mode is set on clean. When its on pushed its awesome for blues but I don't play blues.