300b lovers

If a cool room is important, you want Class D (90% efficient or better) and speakers that are more than 1% efficient (a true Theile/Small 92 dB/meter/watt), as well as switching (not linear) supplies for all the other audio components. That’ll make no more heat than a transistor radio.

Class A vacuum tube is the exact opposite. Constant power draw regardless of signal, from silence to clipping, plus heater current of a few watts per tube, and a few watts of excess heat from the linear regulators. Similar to a 1963 all-tube color TV. My Panasonic 58" plasma HDTV consumes 500 watts, a bit more than a pair of Statements.

To put that in perspective, the same as four or five 100-watt conventional light bulbs, or the heat emitted by two people at rest. A light to moderate additional load on the A/C system, less than 1/10 of its capacity. Of course, if your A/C is running more than 50% to 70% of the time (a 50~70% duty cycle), probably not a good time of day to use the oven or turn on vacuum tubes.

Stereophile published an article on the Westinghouse 300B, which, unlike cheap modern 300B triodes, had a triple coated cathode which lasted longer and was the secret to the better sound. If you can tolerate less power the NOS 45 globe tubes were made the same way and many people find them richer sounding than the cheap modern 300B. 

Around 2005 there was a Japanese 833A SET amplifier driven by 300B transformer coupled to the grid of the 833A and rumor had it the 833A was run on only 1000 Volts with a positive grid bias to force it to draw more plate current. It sold for $350,000, but the parts and labor could scarcely cost a percent or two to manufacture it. You would not need high sensitivity speakers for it, you can use planar magnetic speakers if you want. Lundahl has probably the best coupling transformer there is for coupling a globe 45 to the 833A grid which can run on zero or ground bias for eliminating a bias supply capacitor from the signal path and this is more than enough power for driving less sensitive speakers. Either a globe 45 or a WE 300B will work for this. Hammond makes a more robust air-gapped output transformer rated at higher DC current than smaller more expensive big-name brands and it is perfect for the 833A. 

This is relatively easy to build yourself for less than $2000 retail in parts if you know how to be careful with the 1000 Volt power supplies it needs. 

45 is indeed very very nice sounding.

Cost has gone up quite a bit though. $2k will be barely enough these days for a high quality 45SET DIY project, assuming no fancy enclosures and not using big name irons like ISO or Hashimoto.

Not going anywhere near an 833 or those Eimac transmitter tubes. No thank you. Those things light up a room with a dazzling white light and get serious, room-heater hot. They are designed for transmitter use, with forced-air cooling that ducts to the outside.

And if somebody chooses speakers that are 0.2% efficient, well, what did you expect? Class D or Class AB for you, as well as a dedicated AC power outlet that goes straight to the circuit-breaker box.

@wig Where do you live? I live in Tucson so I'm guessing Phoenix area?