Oxymoron: High powered tube amps that stay cool

A great example is what Dussun is doing with their "Hyper Class A" variable bias circuitry. It's my understanding that they will be releasing a Pre/Power with Stand alone power supplies with 150 watts class A power.

At present, they are utilizing similar circuitry in their V8 integrated. I haven't heard it but it's my understanding that it's a wonderful sounding amp that is extremely efficient. However, I have yet to determine if "Hyper Class A" is a true class A design due to it's level of efficiency. Ping from AAA audio could provide you much mre info than I I'm sure.

http://www.aaa-audio.com/index-products-dussun.htm

Xindak also offers an extremely efficient Class A amp with their XA-6800 SE integrated amp. You'll be seeing many more designs like these coming from China.

http://www.xindak.com/english/products/showditail.asp?id=251

Funny that a country with the absolute worst air quality is focusing on "Green" amp designs.

I have the Berning Quadrature Z's, 250 watts into 8 ohms, and I can put my hand on the grill right above the power tubes and hold it there as long as I want. Now if by cool you mean room temperature, no way, but compared to other tube amps of similar power, they certainly run cool.

Berning ZH270 runs relatively cool for a push pull tube amp. It uses a screen or "grid" drive which allows it to run much much cooler than conventional tube amps. Overall, its very easy to live with and is about as reliable as you can get in this hobby. The tubes last for a very long time too, another advantage to this design. Best if luck.