Low heat alternative to FIRSTWATT J2 ?

OK, I see you are making the distinction between Pass Labs and Nelson Pass's designs which would include First Watt. No problem. The F. W. are definitely a mixed bag of circuit ideas by him.
charles

I borrowed a friend's J2 for two weeks and enjoyed it the whole time.  The case gets fairly warm, but, that is, in part, a result of the whole unit being fairly small in size.  In terms of the total amount of heat being radiated by the amp, I only notices that it was slightly more than that of my low-powered pentode tube amps.  

I have also heard that same friend's DIY build of the First Watt SIT amp.  That was a really nice sounding amp too, but, I suspect it puts out even more heat than the J2. 

I don't know of any solid state amps I like over the sound of the two First Watt amps I heard (although I have not looked extensively at solid state amps).  I heard the Devialet and thought it was okay sounding, but, as with the case of solid state amps, it did not hold my interest the way good tube gear does.  The brand of conventional solid state amps that I find to be nice sounding and engaging is Ayre. 

Any suggestion on J2 vs F6 ? I am considering buying one of them for my 93db Tannoys.

I have also heard that same friend's DIY build of the First Watt SIT amp. That was a really nice sounding amp too, but, I suspect it puts out even more heat than the J2.

The J2, SIT-1, and SIT-2 all have specified power consumptions of 200 watts. (In the case of the monoblock SIT-1 that would be per monoblock). And since they are biased in class A the amount of power they will draw from the wall outlet will be essentially the same at all times, regardless of the dynamics of the music or the listening volume. And aside from a tiny fraction of that power draw which ends up being converted into sound, all of it will be converted into heat and injected into the listening room, mostly by the amplifier but to a small extent also by the speakers,

All of the other First Watt amps have specified power consumptions ranging from 150 to 200 watts, and I’m pretty certain that all are biased in class A. So all of them will inject roughly the same amount of heat into the room (per monoblock in the case of the SIT-1). How hot the chassis gets has no direct relevance to that, and as Larry alluded to in his first paragraph above chassis temperature will vary depending on the physical design of the particular amp.

Regards,
-- Al