set vs otl, which is the most musical

Boa2

Before I got my M60s, my biggest concern was the dreaded heatwave they were purported to throw off. I live just north of what's left of New Orleans where it's typically in the mid 90s both temperature and humidity wise for 6 months of the year. Well, the bad news is that they are mighty toasty but the good news is that somehow it goes completely unnoticed in my no-so-gigantic listening room, come summer or winter. The thermal load just seems to dissipate without leaving a mark. Makes no sense to me but that's the bottom line. I do listen about 11' away from the amps, though. YMMV

Boa2, in response to your question, amps designed for Class A operation all run hot, whether OTL or not, whether tube or solid state. It's the Class A operation, not the fact that they are OTLs, that results in the heat. The best of the OTL amps (Atma-Sphere, Joule, Tenor) are run in Class A for best sound. For a while, Atma-Sphere made the MA-1 and MA-2 models with an optional switch to change operation from Class A to Class A/B to address the heat issue, but I think Ralph dropped that as a standard feature because most owners never wanted to make the sonic trade-off and left the amps set for Class A anyway.

[D]o the OTL's and their little tube armies run especially hot?

I am not a techie, but I think that Howard has put his finger on one of the heat issues. I could be wrong, since I have no personal understanding of circuit design, but I think that large number of output tubes needed for an OTL design, along with the Class A operation, contributes to the heat load. And then all of those driver and input tubes. My Atma M60s each have 12 tubes (so thats 24 for stereo) and my Joule VZN-80 has 16 tubes total (including 8 of those Russian monsters). Put it all together and the heat is an issue, but one I have chosen to live with.

Thanks everyone for the info. We've previously had amps that heated the entire upstairs of our apartment, as well as running up the electricity bill. I think if we had more space, and a quieter AC system, I'd jump at the chance to hear the OTL's. The only one I've heard represents merely a toe dip into the pool of OTL's. Jax2 came through last year with his Berning MicroZOTL, and we ran it through our Klipschorns. Understandably, it's 1 watt didn't lend much weight to the music, but oh my did the vocals sound delicious.