6L6 vs EL34

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. 

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.  

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

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

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