Siemens EL 34

@pehare have you tried GL KT77s in that amp by chance? 

I'm considering searching out a good very good designer/builder to commission and build a nice pair of monos for me in single-ended or parallel-single-ended (if I can find the right builder who is capable of the project with a proven circuit).  To start I would likely use really good EL34s or KT77s. More than a few friends have run the newer KT77s at my suggestion and all of them see quite pleased.  Maybe a little more power and retaining a bit of that 34 velvet.  Will be interested in your feedback on KT66s in Will's amp later on if you try it down the road. 👍 

decoony, no I have not tried them.  I'll probably play it as is for 6 mos. or so before I try different outputs.  Yes, I've ready somewhere that the Upscale Audio folks recommend KT77's as an upgrade in EL34 based amps.  

There's a minty pair of AES/Cary six-packs for sale on Ebay and craigslist not too far from my area - have you by chance tried those?  Too many output tubes for me but I've heard they're great sounding.

@decooney I tried Gold Lion KT77's back when I owned a Music Reference RM9 MK2.  I preferred Gold Lion KT88's and Siemens EL34's in this amp, as the GL KT77's lacked emotion and just sounded too clean & lean in my experience.  YMMV.

@pdreher

i’m curious, in your comment below, are you referring to modern day production russian made gold lion kt77’s -- or -- the true-blue old stock british gec/mo-valve/genalex gold lion kt77’s?

in my experience, i still find the real deal british kt77’s to be the absolute pinnacle of all el34 equivalents, a step above even british mullard or dutch amperex el34’s.... silky smooth yet extended highs, dense yet tactile and delicate midrange with a beautiful spotlighting effect, and terrific control and slam down low (which the mullards lack to a degree) ...

FWIW…the best I’ve ever tried the New production “Tung Sols” EL 34 B.  It is a superb tube…and made my musical reference RM9 MK2 sound glorious.