Tube Watts vs. Solid State Watts - Any credence?

10-10-15: Djfst
Tried it again and the 8ohm taps definitely sound better all day long compared to the 4ohm taps. Who knows?

there's a good explanation for it as stated in my earlier post. I guess you missed reading it??

Bifwynne,
yeah LOL! ;-)

@Bombaywalla ... do you understand the term "[o]utput stage coupling is a combination of “ultralinear” and Audio Research’s patented “partially cathode-coupled” topology ..."?? I have a rough understanding of ultralinear .... No clue about "partially cathode-coupled” topology. Any idea??
Bifwynne

well, this is a serious case of the blind leading the lame but I'll give it a shot. I hope that somebody who knows more steps in....
'ultra-linear' is a global negative feedback technique where, in a tetrode (4 active electrodes) or a pentode (5 active electrodes), some part of the output (usually present on the anode or plate) is fed back to one of the screen grids of the tube. The amount of output signal fedback depends on the tube type (KT88, 6550, 6V6, etc). David Hafler has patent on this where he fed back 43% of the # of primary xformer turns to the screen grid to linearize his amplifier. What this global negative feedback did was reduce output distortion, reduce output impedance & raise the output power to near-pentode levels.

'cathode-coupled' is a tube amplifier topology where the input tube is cathode coupled to the next gain stage tube. here are some pix for you to look at (you can drag your mouse over the pix without any harm. Click on the pix at your own risk!)
http://www.bing.com/images/search?q=cathode+coupled+amplifier&qpvt=cathode+coupled+amplifier&qpvt=cathode+coupled+amplifier&FORM=IGRE
the 1st pix itself should be good enough to allow you to visualize what I wrote.
In the pix the 2 tubes are strongly coupled as there is a deliberate connection between the 2 cathodes. The issue with this amp is that the cathode of the input tube is at a very different voltage than the cathode of the 2nd tube. So, this amplifier becomes very sensitive to power supply variations & noise. Thus, I'm *assuming* (you know this goes!! ;-) )that ARC has a patented technology where they partially couple the 2nd tube to the 1st tube so that they can make the cathodes of both tubes operate at nearly the same voltage while still transferring the input signal to the 2nd tube to amplify it.
I could be out on a limb here.....

tube amps have no bass hence it's power mostly applied towards mids and highs while the solid state amps go full range. 70w of tube amp power will scream out louder on mids and highs, while same of solid state will cover full range and will have substantially lower volume vs tube. otherwise power is just product of voltage and current not just watts.

Thanks Bombaywalla ... but what is the purpose of partial cathode coupling. Is it a form of local negative feedback?? Does it ameliorate some of the adverse affects associated with NFB that Ralph has written about, e.g., TIM distortion that raises the level of odd ordered harmonics??

ARC has used this type of topology for many years.

Czarivey ... I think your post slaps quite a bit of paint with a very wide brush.

My ARC Ref 150 SE has a relatively low output impedance, resulting in a damping factor of 14 (assumes an 8 ohm load; would be half if the load is 4 ohms). That ain't bad for the bass. In addition, it has a 1040 joule power supply, which helps the amp to muscle its way through demanding loads where serious current (and correlatively power) is needed.

And based on my own ears, I do not concur that my tube amp "has no bass" or that its power is "mostly applied toward mids and highs." I surmise that Ralph (Atmasphere) would take similar exception about his highly regarded amps.

Music requires very little average power, unless one listens to sine waves. It is possible that two of 50W amplifiers can be designed with very different headrooms. One might have small headroom being, for instance class A amp while the oder has huge headroom with average power limited only by size of power supply and heatsinks. Amp with higher headroom might appear much louder without distortion.

14dB is rather shallow feedback.

Damping factor of 14 is OK. 8ohm speaker's impedance is mostly resistive. Assuming, that it is approx 6 ohm it limits effective DF to 1.33 . Amps DF of 14 will make it worse only by 9.5% - irrelevant.

There is a lot of local NFB in almost every amp. Any resistance in cathode is a form of NFB. Global NFB doesn't have to create TIM if it is applied within certain limits. It improves pretty much everything - bandwidth, output impedance, THD & IMD. Great sounding amp with small amount of NFB requires great design and quality components. Unfortunately it is cheaper to achieve the same using cheaper design and excessive amount of NFB hence creating overshoots (odd harmonics in frequency domain) and unpleasant bright sound.