Tube Watts vs. Solid State Watts - Any credence?

10-09-15: Djfst
So a followup question - if 2 amps both have 140 watts, why ever buy the more expensive amp if you are paying for wattage? Most have indicated quantity of wattage, but can the quality of wattage be better in some amps than others?

The more expensive amp has a more robust power supply which most probably allows that power amp to double down with each halving of the load impedance. This means that the more expensive amp also has more current delivery capability which in turn means that it can power hard-to-drive speakers far more easily than the less expensive amp.
This is based on the assumption the you are not comparing 2 very disparate brands i.e. both amps are of brands that have similar reputation & command similar prices in the marketplace.

10-10-15: Inna
I don't remember where but once I read that someone was comparing the sound of 100 wt Gryphon with 600 wt Krell, both transistor amps. Same speakers,forgot what that was. Besides sounding a lot better in every respect, Gryphon also sounded more powerful. Dynamic speakers, this I remember.
What are the possible explanations?

the above is an explanation for your question Inna. In this specific case the Gryphon doubles down all the way to 1 Ohms. One of the rather rare s.s. amps in the market & very expensive. My friend used to own the Antilleon Signature which was a 100W/ch amp but was 800W/ch into 1 Ohms. Beuatifully built amp - like a tank & almost no speaker could ruffle its feathers (but don't hook an ESL to this amp as it was not meant to drive an ESL).
Current delivery into a speaker load is very important esp. when it comes to hard-to-drive speakers (which are characterized by having wild impedance & phase swings).

Secondly, how can low powered tube amps sound so much better with some speakers that have amp recommendations much higher? Very few tubes get over 100 watts, yet are very prevalent even on some inefficient speakers. Any thoughts? Just trying to learn more.
Djfst

Atmasphere explained this quite clearly in his post above. Did you miss it?
it's the distortion characteristic of tubes amps - when they're overdriven a little the distortion is more pleasing to the ear than a s.s amp that is overdriven the same amount.

I know tubes have there own characteristics, but besides that, from a power standpoint, would it be better to go to KT120s to get more power to my speakers? Would the difference in wattage moving from EL34s to KT120s (15 watts increase in ultra linear, 5 watt increase in triode), be beneficial or even perceptible to my ears? Would this be better for the performance of the speaker, or at least the health of the speaker?
Djfst

in the end it really depends on what kind of sonics you prefer.
Tube amps using ultra-linear mode of operation use a lot of global negative feedback to generate a higher wattage. These sort of amps have a very robust sound & trend to sound more like s.s. amps. And, behaviour-wise they also behave like constant-voltage sources (which most s.s. amps can be characterized). I've found that ultra-linear tube amps had more bass punch but their mids & highs do not have the delicacy that is often associated with tubes.
Operating an EL34 in triode mode would be operating this tube in as linear a mode as is possible. Remember the EL34 is a pentode tube but in triode mode it operates like a tube with 3 units (sorry I could not think of a better word at this time!) - anode, cathode & 1 screen. You get much less wattage (as you have stated) but you get a beautiful tube sound that trends towards the type you hear from more traditional triode tubes such as 300B, 2A3, PX25, etc. At one point in time i used to own an AES Sixpac that had 6 EL34 per chassis & output 60W/ch in triode mode. It was a very addictive & beautiful sound. That amp drove my then-speakers with plenty of power - didnt have the bombastic bass of a s.s. amp but i did not care as I got much more from that amp that compensated for a less bass response. When I changed my speakers that amp had to go. Personally, I'd go for linearity hence triode mode. But like I wrote before - you might like you music delivered differently.....

10-10-15: Ebm
Wow thats a tough one i was up all night thinking about that!!

EBM, I'd like a different snidy punch-line. I've laughed at this one one too many times! Search your sarcastic brain for a new snidy remark. Thanks.

The manufacturer recommends 50-180 watts and received wisdom seems to be that the speakers respond better to solid state watts (what does that mean)?
Mikey8811

I've not looked at the Vienna Acoustics Kiss speaker impedance & phase plots but if this is the wisdom that has been imparted to you then it would mean that the VA Kiss has some wild impedances & phase angles in the bass region where the actual impedance is quite low where a tube amp would have difficulty sourcing large amounts of current to have a controlled bass response. In such a case a s.s. amp would do better esp. if it can double down for each halving of the load impedance. This would be an expensive s.s. amp since it would have a very robust power supply. Heavy chassis, heavy power xformer, large heatsinks, high cost but it would give you a tight bass response while a tube amp would give you flabby bass response unless you spent $$$ to get a large tube amp.

10-09-15: Djfst
High end audio is definitely tricky. For example, I'm running a Primaluna Dialogue HP Integrated Amp with EL34 tubes to Sonus Faber Olympica III Speakers which are 91db efficient and are 4ohms rated according to specs. The Primaluna has 4ohm taps and 8ohm taps, and the 4ohm speakers sound far better on the 8ohm taps.

I found your speaker measurements here:
http://www.soundstagenetwork.com/index.php?option=com_content&view=article&id=1285:nrc-measurements-sonus-faber-olympica-iii-loudspeakers&catid=77:loudspeaker-measurements&Itemid=153
if you scroll down & look at the 2 plots "impedance magnitude variation" & "phase angle" you can see that this speaker has capacitive phase angles in the bass region to, oh, ~150Hz. The impedance is complex i.e. has a x+jy sort of form. So, the real part of the speaker impedance into the power amp is delivering current is not 4 Ohms as printed on the back of the speaker but less than 4 Ohms due to the capacitive (reactive) phase angle. So, any power amp would be asked to deliver more current than originally thought (since you are thinking it's a 4 Ohm speaker) & this can tax the power amp.

When you connect your SF to the 8 Ohms tap, the power amp is being asked to deliver more current into the lower (4 Ohms) speaker impedance compared to when you have it connected to the 4 Ohms tap. The higher current delivered yields a better bass response.
The plots show the speaker is mostly inductive in the 150Hz-2.5KHz. So, when high voltages are present in the mid-bass-to-mid-range little current is asked from the power amp due to this inductive impedance nature of this speaker in this region (the math omitted deliberately). And, in the high-freq even tho the speaker become capacitive there is not much energy in those frequencies so the power amp is not taxed much.
So, it seems to make sense that this SF speaker would sound better on the 8 Ohms tap.