I have some limited experience with EL34/6CA7 tubes. My two favorites are vintage Sylvania or GE "fat boy" 6CA7, and new production Genalex Gold Lion KT77. The vintage 6CA7 fat boys are well-balanced with a great midrange, full (with good but not great detail) bass, and smooth highs. The GL KT77 have more detail through the mids and highs, I find them to be very good on highs as I like good detail and imaging, but some tube enthusiasts find them overly detailed and more SS-sounding. If they ever quit making these, I think they will become highly sought after and expensive.
The JJ KT77 is decent and is much less expensive. Quite affordable. Also affordable, but I haven't heard them, is the Electro Harmonix 6CA7, a "fat boy" type design. I've read good things about them considering their price.
Many people sing the praises of the Psvane & Shuguang upper end EL34 tubes. Haven't heard them, pretty pricey.
The Gold Standard is the Mullard EL34 xf1. Good luck on finding any. Bring your wallet.
