Understanding Tube Power Ratings

I had more success running my 2.2's on 45 tube watts (C-J) than on 70 (Classe) or 100 (NAD) SS watts. Now I have them on 200 tube watts (VTL) and they're even better (this isn't a parable though - my SS amps weren't of comparable cost or quality to yours, or to my tube amps). The 2.3's are a little more demanding than my speakers, but for average listening levels in an average-sized room, I would imagine that good 100-watt tube amps could contend. Stick with beefy power supplies and output transformers, and leave maximum rated power to be influenced by how loudly you like to listen and your room size. (For an amusingly perverse take on the conventional wisdom concerning 'doubling-down' and SS vs. tube power, check out Ralph Karsten's white paper on the Atma-Sphere website.) Bottom line: Sound quality is difficult to directly correlate with power ratings (and that goes in both directions!) or choice of active devices (tubes or transistors) - better to trust your ears.

Sean: Since tube amps, as a rule, don't 'double-down' as some SS amps can, but are certainly capable of sounding just as good, why do people focus on this aspect of SS amp performance and not of tubes? Is the fact that this capability doesn't seem to reliably correlate with sonic quality indicative that in the real world, most good-quality and properly-matched amps are not being called upon by actual speakers and listening styles to test their ultimate limits in the current delivery department, thus obviating the distinction? (In other words, at listening levels comfortably below the onset of clipping, even tubed amps are putting out all the current being demanded of them into varying speaker impedances when playing music?) If true, pure voltage-source behavior into static loads using typical test signals at maximum rated power would seem to be a red herring of a specification for anything other than offering bench confirmation how over-built any particular big SS bruiser may be - not a bad thing, but maybe not the most important or telling of qualifications either.

Agreed Sean, I wouldn't think tubes first if I had a low-impedance, multiple-woofer, highly reactive load to drive. I'm more just curious about the audiophile psychology when it comes to this type of spec (and anyone can feel free to chime in on the subject).

Surely we've all noticed how an amp's ability to 'double-down' - or even the illusory capability of it, engendered by fudged specsmanship (where the output capabilities of a SS amp into a 2-ohm load is presumably taken for the baseline figure and then successively halved into each doubled nominal load, thus underreporting the amp's 8-ohm capabilities in order to make the amp appear completely load-indifferent) - is trumpeted for SS amps and ignored for tubed amps.

Yet no mention is ever made of the obvious fact that this supposed attribute or deficiency, depending on which direction you're coming from, apparently makes very little to no actual sonic difference in most 'normal' set-ups. I mean, it's not like in most systems, a good tubed amp of appropriate power rating is going to fail to transmit the bass frequencies or something. Still, many audiophiles will schizophrenically look down their noses at SS amps which admittedly can't 'double-down', while at the same time holding tubed amps to a completely different standard where this ability isn't even a consideration. I am proposing that there may actually be a pretty good reason for the latter phenomenon: 'doubling-down' is apparently an ability that normally won't make a predictable sonic difference in the real world.

Presumably, this would be because most good tube amps of appropriately-matched power ratings, used with most typical speakers at common volume levels in average-sized rooms, will still be able to supply all the current demanded of them throughout the spectrum, regardless of the speakers' varying loads. Ralph Karsten (see my previous post) takes glee in proposing a divergent view of the situation as it applies to his own OTL tubed amps: he chooses to fault SS amps for wimping out and providing less power as impedance rises - instead praising tubed amps for putting out relatively constant power (discounting the effects of matching the output transformer to the load, since of course his amps don't have output transformers) across a broad plateau of load impedances. He also says, in effect, watts are watts, and most speakers won't even come close to demanding all the current theoretically available from the big SS arc-welders: power draw at normal volumes, as determined by common speaker impedance and sensitivity ranges, and as supplied where Watts = Amps x Volts from any type of amp, will virtually never exceed the current-delivery capabilities of a sufficiently good tubed amplifier. He winkingly asks, Should we truly want varying power into varying loads, or should we really want constant power into varying loads?

Actually, for myself, I suspect his argument is at least as much sophistry as the 'doubling-down' one. To me, the real issue is likely that how any amp responds at its maximum rated average continuous power limits is largely beside the point, since if it is correctly-matched with the system, room, and desired volume level, it will be running well below its maximum average continuous power limit, and thus won't be called upon to deliver more power than it can supply when actually playing music. In other words, whether an amps responds by supplying 200w at 8 ohms and 400w at 4 ohms - or 200w at both (or 400w at both) - at its maximum average continuous output limits when playing a static test signal, is largely immaterial when the question in the real world is: Can such amps supply a few watts of averaged continuous output power with occasional brief peaks an order or two of magnitude higher when playing music into a load that varies? For most systems and listeners, the answer in both cases, tube or SS, will probably be yes, thus rendering any amp's abilities with continuous power demands not found in the real world academic - and thereby explaining why we don't actually hear the maximum rated continuous power-into-load behavior of either type of amp as being a sonic liability as long as it's up to the job at hand.