recommendations for amplifiers that don't emit tons of heat

glennewdick---As you say, KT88 filament current is specified as 1.6 Amperes. The related filament voltage is 6.3 Volts. That's TEN WATTS of power dissipation that's consumed merely to "light up" the quiescent KT88 vacuum tube. In that state, the tube is merely at passive idle; it's not doing any functional amplification. It's serving only to emit heat + dim illumination. Additional power is then consumed when the tube is subsequently biased to pass current from cathode to plate. That's truly archaic efficiency.

Yes---and 1.6 A. x 6.3 V. = 10 WATTS.

And that power is consumed merely to "light up" one KT88 to a quiescent state, where it does nothing more than emit 10 watts of heat and light. Additional dissipation, over and above this wasteful filament dissipation, is required to perform active amplification.

the biggest power consumer in a tube amp is usually the heaters for the cathode

This statement is rarely true- I think the exception used in audio is the 6C33. For most power tubes - like a KT88- the heat made by the cathode is insignificant compared to the heat made by the tube as a result of plate current though it (its class of operation).

As a result, compared to a solid state amp of the amp power and **same class of operation** , tube amps will make marginally more heat.

If you put a tube amp in standby (no B+) even after sitting there all day the tubes won't burn you (the exception being the 6C33). But after being on only a couple of minutes the same tubes will be much hotter if B+ is also applied!

The problem is that if a solid state amp can't bring home the bacon, then it really doesn't matter how much heat it makes. In high end audio, the **sound** produced is the goal. 

Trig you fail to mention what is your budget and what is the rest of your system. 

There are tons of modern amplifiers which will best a  Krell KSA 150 it depends on system matching to what amplifiers will work for you.

We have the Nuprime ST 10 which is a 150 watt compact analog switching amp and it sounds fantastic much better than most Class D amplifiers and it is tiny and gives off much less heat then a big Krell, the bass conrol on the Nupirme is fantastic. 

Howerver that amplifer will not sound as good as many of our larger more conventional amplifiers. So again it is going to come to budget. 

The best amplifier in the shop a T+A PA 3000 gets warm but never super hot and that amplifier will run rings around Dan's newest designs. So it all comes down to level of performance you want to get and how much you are willing to pay for. 

Dave and Troy
Audio Doctor NJ

I can strong recommend two amps. The B.M.C. M2 monoblocks have fans but very  quiet ones. In balanced XLR and the Koda K-10, they are great!

The other is the H-Cat X-11 amp with automatic focus. It has heat sinks on back. I live in Texas and have had neither of these amps heat up my room.