Well Tommy... lets continue with your theory.
A Sunn 200s will put out 60 watts with two 6550 tubes. Therefore an SVT with six 6550 tubes should put out... 180 watts... only 3 times as much. Right... perfectly logical. What do you mean that the SVT is rated at 300 watts??? NOT POSSIBLE!!
What you are missing... is the voltage that the tubes are operated at. I don't exactly deal with SVT's, but I do know that the voltage is higher than what the Model T design operates the tubes at...
And in another post... I mentioned that the RMS power rating is also related to the current capability of the power supply. Voltage times current = power in watts.
I don't think I would consider the 150 watt rating of the Model T to be conservative... as in stating less power than it is really capable of. If you look at the notes in the schematic available on this site, the power output measurement is stated as something like 24 point something volts across a 4 ohm load... with specific control settings (all up?).
If you take the voltage across the load (speaker or dummy), square it, then divide it by the resistance of the load, you will get watts. So, in this case, 24 point something times 24 point something divided by 4 equals as close to 150 watts as you are ever going to get.
Sunn was rather conservative, as in the way they operated their amps, and they did that by the design of the amp. All circuits were operated within what is commonly called "design maximum" specifications for the tubes they used.
Even though those specifications are called "design maximum", it doesn't mean that they can't be exceeded. A perfect example of that would be Fender's Deluxe Reverb that operates the pair of 6V6 output tubes way above design maximum to achieve 20-22 watts RMS of output power. The Princeton Reverb, also using a pair of 6V6 output tubes only achieves about 12 watts RMS. The circuit is operated closer to design maximum specifications than the Deluxe Reverb.
The trade off for more power achieved by exceeding the design maximum specifications, is shorter tube life. Even Mil Spec 6V6's in a Deluxe Reverb have a short life... and some brands only have enough lifetime to be able to gasp their last breath when the standby switch is turned to the on position.
Loudness of an amp is not directly related to it's power output.
A long time ago, I lived in El Paso Tx and went to a concert featuring a group called "Vanilla Fudge"... some of the older readers out there will remember them.
Anyway, after the concert, there was a writeup in the local paper about how some local guitar player loaned his Marshall 100 watt stack (two cabinets) to the lead guitar player for this concert. I can't remember the lead guitar players name... but he had a comment in the article... he only had a Fender Twin Reverb, and really appreciated the extra power of the Marshall 100 loaner for the concert.
I laughed my A** off. You see, his Fender Twin Reverb (a Silverface model) also had a power rating (RMS) of 100 watts RMS. The 6 extra 12 inch speakers in a stack configuration (of the Marshall) only gave him better dispersion of sound... not more power. Better dispersion of sound can sound louder depending on the characteristics of the "room". The El Paso County Coliseum, hosting many concerts that I went to during those days, does have a good acoustic response.
Tim Bogart... the bass player of Vanilla Fudge, seems to have always understood this principle. He always used a stacked set of cabinets - this concert it was three Dual Showman cabinets. Two on the bottom upright and at a V angle, with the third stacked on top of those two.
Wattage is only a calculation. The rest of the system determines the other things like loudness. In much the same way, horsepower is only a calculation (torque times RPM/5252)... but in drag racing, the car with the higher torque at lower RPM will always beat the higher horsepower car off the starting line. The higher horsepower car only hopes he can make it up before the finish line.
Sorry for the rambling, but I hope this helps!!
