Ruby's are okay depending on the circuit. I would simply use a quad of EH EL34's. The slim one's. I have had some manufacturing buddies tell me they don't like the Fat Boys as much. The EH's have an extended top end and an articulate midrange.
I have a modified Dynaco ST 70 and the EH's are my tube of choice for that amp. I have tried Sovteks, JJ's, and I have a Quad of Teslas but they are the newer vintage and are almost equal to the EH's. By the way I purchase my EH EL34's exclusively from Jim McShane. I tried several other vendors but I'm happy with what I get from him.
Most importantly is that I have a pair of Mullard Reissues brand new with about 20+ hours on them which went in the Dyna first. I thought they were too soft sounding. I bought a pair of EH's to compare and what I got was a sigh of relief. The sound was more effortless than any of the other tubes I tried. I like the warm sound but I also want detail and articulation. I don't like that warm sound with my Spica TC60's.
I have a pair of Quicksilver 8417's that were modified for KT88, 6550's, etc. I recently found out that I could run EL34's in it. I put in the Mullards at first and they were pretty darn good. But when I put the EH's in there it I got a smoother and more articulate sound. More transparency if I must say.
I have a friend that bought several quads of NOS tubes and they were wonderful but when one went up smoke glowing red he was hurt and finding a match was a chore. I told him to buy a pair of EH's and he did and he was very impressed. He wanted buy a Quad of Gold Lions. But I told him he could buy 3 Matched Quads of EH's for the same money. The EH's sound was at least 95% of the gold lions. His amps were a pair of VTL monoblocks and A quicksilver GLA. Until I find something that betters the EH EL34/6CA7's I'm sticking with them. None of the other recent vintage tubes are as articulate in either of my amps the Quicksilver 8417's or my Dynaco ST70. Plus the EH's are comparable to the Ruby's in cost. Give them a listen.
