Tube amp heat questions...

Probably has more to do with how the amp is designed in the first place and how far the design pushes its tubes to develop its rated power. For example you can get 80 watts out of four 6550 tubes but they are close to max output. The same tubes in a design that produces 40 watts will run its tubes cooler and they will last longer. But it is fair to say, I think, that the more power your amp produces the more heat it will produce, either in how many tubes you need or how hard you have to push the tubes. Moral of this story is if you don't absolutely need all that power why buy it in the first place.

FWIU, the following points all have an impact on either the WPC and/or the heat generated.

~The class of operation (single ended, push pull).

~The type and configuration of the output tubes (triode, tetrode, ultra linear or pentode).

~The number of (mainly) output tubes.

~The amount of bias and plate voltage on the output tubes.

~The type of bias on the output tubes (fixed or cathode).

The bottom line is that tube amps of comparable or lesser wattage have far more excess heat than all solid state amps with the possible exception of a pure class A solid state.

Even less heat is generated by SS class D amps.

First, congratulations on your purchase, and welcome to the ranks of happy tube amp owners :-)

As the others have indicated there are many design-related variables that are involved, so the short answer to your well put questions is "no."

A longer answer: The amount of heat generated by the amplifier itself will be proportional, at any instant of time, to the amount of AC power going into it minus the amount of power being delivered to the speakers.

However, since with nearly all speakers that are intended for use in the home the great majority of the power going into them will be converted by the speakers into heat, with only a small fraction of that power being converted into acoustic energy, it is reasonable to approximate the total amount of heat generated by the amplifier + speakers as simply being proportional to the AC power drawn by the amplifier.

The relevant specs on your VSi55, for example, are as follows:

POWER REQUIREMENTS: 100-125VAC 60Hz (200-250VAC 50Hz) 320 watts at rated output, 500 watts maximum, 205 watts at "idle". 0.5 watts power off.

So you can project the amount of heat that would be generated by the amplifier candidates you consider for the second system by comparing their specified AC power consumption with the 205 to 320 watt range your present amplifier has under normal operating conditions.

If some of the candidates don't publish AC power consumption specs, ask the manufacturer if they can supply those numbers.

Finally, keep in mind that under typical circumstances an amplifier will be called upon to approach its maximum output power capability just on infrequent dynamic peaks. So most of the time you are probably operating the VSi55 such that its AC power draw is much closer to the 205 watt number than to the 320 watt number.

Enjoy! Regards,

-- Al

Wow, fantastic information, thanks everyone. I had a suspicion that I was probably oversimplifying, so I'm glad I asked. There's good info in every answer, thanks to all.

Newbee, your point about buying only the power needed is very pertinent. I'm driving a set of B&W PM1, with 84dB sensitivity and they dip to 5.1 ohms. I went to the dealer to look at a Rogue Sphinx, certain that I needed every bit of their 100wpc (if not more) to push the B&W (my Marantz integrated with 70wpc did not match well at all and ran out of gas). The dealer showed me the Sphinx, then the Cronus Magnum with 90wpc, but insisted I also take a listen to the pre-owned VSi55 he had just taken in, with brand new tubes. I almost made the mistake of dismissing the ARC thinking that 50wpc would be a backwards step and waste of time and money, but I'm glad I listened to him. I'm too inexperienced to understand the technicals of why 50 watts of tube power opens up the B&W and pushes them to insane volume levels while the music remains perfectly clear and listenable, while 70wpc of solid state power turns to aural chaos at anything above 1 o'clock on the dial - I'm sure the Marantz is a superb integrated, and it was just a bad match-up. But the lesson I learned is that there's more to the story than just absolute WPC.

I like the thermometer gun idea, Viridian.

Jjrenman, your point about Class-D is duly noted - when summer heat rolls around, having one for back-up duty may save me electric bill $$ and make my den bearable if the ARC just gets too hot.

Al, thanks for the layman-friendly explanation - I needed it!

Eric