I don't have a Rogue amp so can't speak for synergy there. I have had three or four different amps that utilize EL34's so can say a few words about my experience with tubes. For current production tubes I'd go with JJ/Teslas or Electro Harmonix. The JJ's in early vintage 90's form were one of the best current production tubes having won the Listener Magazine EL34 shootout back then. Mullards are considered some of the best NOS tubes but are pretty darn spendy and if you're getting NOS make sure you are dealing with a reputable dealer. I like Jon at The Tube Store http://www.thetubestore.com Great guy, knows his tubes, good prices, fast, efficient, and has given me consistently GREAT customer service. Be careful with venues like eBay as you can drop some serious money on tubes there and have no idea what you are actually getting. Bargains can be had, but at some risk. I'm currently using vintage JJ/Tesla's in my Quicksilver Mini Mites in my work system. Great tubes! I'm told in those particular amps that they sound even better with good KT88's in place and will throw a broader soundstage. EL34's are a very musical and dynamic tube in all the applications I've heard them in (I've owned four different amps that use them: Jolida, Mesa Baron, and two different Quicksilver amps). I've never found them overly warm, nor overly analytical, nor particularly airy. They've always occured to me as a nice musical, middle-of-the-road kind of tube. Give Jon a call at The Tube Store, or send him an email, and ask him what he thinks of that tube in your amp. He's given me some good advice. I actually didn't like the EL34's as much in the Baron (uses 12 of them). I found it too punchy and more SS sounding than I wanted. I was going to buy some different EL34's but, after talking to me about what I was looking to achieve (a more traditionally tube-like warmth and air) Jon suggested I try the Svet 6L6GC's instead. He was right on the money and I was very happy with those tubes in that amp. Although the amp still ultimately was too SS sounding for my tastes - the 6L6's were a big improvement nonetheless. I don't think there are any rules here and what works for one tube application may have a completely different results in another. As usual, YMMV!
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