6L6 vs EL34

It was pointed out to me the other day that it would be easy to convert my amp, a stereo PP EL34 amp, to run 6L6's. I've never really listened to the 6L6 tube before do any members have any thoughts on 6L6 tubes vs EL34's? I am running the Genalex KT-77 re-issue tubes in my amp and love how it sounds now. Thanks!

@noromance Nice those must sound amazing currently listening to a very smooth quad of 80s Svetlana 5881s.

I've a quad of NIB NOS 1960s Tung Sol 5881 that I've never listened to. Some day...

Listening to a 5881 amp now from Synthesis and really enjoying it, can take 6L6 tubes also.

I am a fan of the 6L6 tube, and a bigger fan of its cousin—the 350B (crazy expensive but good sounding).  Another similar sounding tube is the KT66.  

As an amplifier designer I can tell you that both 6l6 and el34 can be awesome. There are a  couple of things to consider. 1 el34 s need substantially more current for the heaters.  2 the bias is a little different.  3 el34 is a pentode while a 6l6 is a tetrode  connected pentode. In all my designs I make provisions for rolling both. Leaving the choice to the particulars of the client. Also the speaker driven. 6l6 dose it's finest with an oversized matching transformers and  cliptch or infinity.  While el34 is the thing to have with Polk audio or bose 901. I still recommend an oversized transformers just gives better bace and a more polished sound. 

Conversion is
changing 1 resistor in the bias circuit, changing screen grid resistors (if applicable), then bias it w a scope.
But you an change from EL34 ,6L6, KT66, 6550,etc. pretty easily.

EL34 being the European hi fi tube, specifically made for music.
6L6 being a home version of military (5881) amplifier tube.

But KT77 is already pretty sweet. I don't think there's going to be a huge change by swapping to EL34.
6L6: that's better for guitar amplifiers. Not really a hi fi tube, but Telefunken is selling them now for broadcast etc.anyway.
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Im lucky, I can use many different output tubes in my amps....  I've had 5881, 6l6, KT88, KT66....  and I keep going back to EL34.   They all sound good, I guess I just prefer the EL34 tone.     I would like to try some KT77,  just retubed to Mullard repops so maybe down the road.
Al thanks as always for your technical knowledge and trenchant comments. The conversion idea hadn't gotten past the musing stage and Vu and I haven't seriously discussed it so we haven't gotten quite that far. These guys design and build great sounding reliable gear, including amps using the 6LG tube so I am assuming they do know of what you speak. But good to have that knowledge for myself thank you!
Jon, there are considerable differences between the technical parameters of the EL34 and the various versions of the 6L6, many of them in the direction of the 6L6 not being able to handle voltages, currents, and power dissipations that wouldn’t be too high for an EL34. That is particularly the case for 6L6s which precede the version that has a GC suffix.

I assume the person who suggested the conversion is aware of these things. But depending on the design of the amp and the nature of the conversion choosing a 6L6-GC rather than earlier versions (i.e., 6L6-GB, 6L6-GA, 6L6-G, 6L6 no suffix) may be preferable or even necessary, and may result in greater longevity of the tubes.

Good luck. Regards,
-- Al

@trelja Yes we are and Vu has the best ears of anyone I know and I always go with his opinion. Just need to give it some thought as I am really happy with where the system is now. And I love this amp, Pavel to me built some amazing sounding amps for Vu and some indestructible ones. I feel like I really lucked out landing this amp and always want to consider any changes to it. And I bet you wish you still had that 45/2a3 push-pull between you and me pretty sure i saw a pair of 45 pushpull monoblocks there this weekend :) I am sure those Quads sound amazing pretty sure you're powering them with Jadis now?
@jond, "Heard from Vu in his opinion 6L6 warmer and to him more musical at the expense of a bit of power."

Sounds like we're of the same mind.  As folks have mentioned, there's a diversity of opinion.  As I like to say, that's why they make vanilla AND chocolate.  Like most of us, you never really know until you listen for yourself, and draw your own conclusions.

By the way, as we've discussed previously, you have one of Vu's what I'm sure is phenomenal EL34 amps.  I had one of his 45 / 2A3 push-pull amps.  In many ways, it was possibly the best amplifier I paired with my Hornings when I had them.  I also got my beloved Quad ESL57 from Vu
Heard from Vu in his opinion 6L6 warmer and to him more musical at the expense of a bit of power. He also says vintage 6L6 tubes are readily available and sound great. I will certainly give it some thought I've got the system rewired with copper all the way through now Kondo>Auditorium23>Audio Note UK and I like where the sound and tonal balance are not sure if a change would be too much of a good thing.
Perhaps tonal differences might depend on the brands of tubes we are comparing. I've mainly used SED 6L6GC's , SED EL34's, Tesla E34L's (both old pre war-stock and new) in Sonic Frontiers and Primaluna Dialogue amps. FWIW.
In this hobby I am always amazed at the variety of results obtained from the same product(s) by different users.
If you do change your amp, please post your impressions.
Also, could you identify the amp being used?
@mechans  +1

As usual, I will side with my very close friend, The Doctor (Mechans).  He stated things perfectly.  6L6 more lush and thick, EL34 more forward, engaging, and detailed, though not at the expense of sweetness or sounding harsh
Thanks mechans that jibes with what i was told previously. I guess it's amp dependent so we shall see.
Not my experience at all, but then again the sound always depends on the system the tubes are in.  EL34s 6CA7s and KT-77s have all sounded very clean and precise.  The 6L6 has always been a sweeter more euphonic tube, but as I said the amps they were in I think contributed a great deal  to that sound.
Interesting guys food for thought. Waiting to hear what Vu thinks I may do it.
+1 re jadedavid's comments. That's how they sound in my amps. The clarity that they offer can be addictive depending on your sources and speakers inherent sound.
jadedavid thanks for your input it's very interesting I was told that 6L6's would sound sweeter by the person who suggested the conversion. I guess as you said YMMV.
Generally speaking, in the amps that I have heard, the 6l6's are cleaner and more accurate. Whereas the El34's are warmer and richer. YMMV.