how much tube power is needed?

Not meaning to confuse the issue here, but I noticed reference in the responses to 3dB being a level difference where doubling the power is necessary. This is true of course, but I wanted to point out that it takes about 6 to 7 dB of boost to double the PERCEIVED LOUDNESS (for the midrange of the music spectrum). This translates roughly into QUARDUPLING the amps power output to double the perceived loudness for a given speaker. Many feel it's the FIRST watt of output that counts most toward listening satisfaction, and those in the Triode camp take pleasure in that. Hope this is useful.

In counterpoint to Bottlehead's response, some studies have shown that as little as a 0.1 dB difference IS perceptable. Meaning that in an A vs. B choice (this is the same system, but that one choice has 0.1 dB less attenuation), the louder-by-0.1dB choice was preferred because it "sounded better". As far as the "first watt" is concerned, this may be perfectly true for tube amps: Less than 1 watt is dominated entirely by noise, and more than a few watts has high harmonic distortion! So these amps may ONLY sound reasonable when outputting one watt.

this is in response to fotopress . He claims that no tube amp can drive your speakers properly. I am quite sure that a large VTL,AR or CJ would beat hands down ANY 100 watt transistor amp.Now to facts.I am driving electrostatic Acoustat 2+2 with a custom built tube amp(full triode parallel single ended class A 60 watt)to measured levels of 105db peaks without clipping or distortion.My room is comparatively large(12X20 feet).The sinus wave is perfect(measured on the speaker terminals)at all listening levels and with all kinds of music.Measurements are very good even with Sonus Faber electa amator loudspeakers.Hopefully,in about three weeks i will do the same on a friends Martin Logan SL3

In response to user35@ibm.net, I fully agree that a 60 watt tube amplifier will drive the Acoustat 2's to 105dB peaks, but maybe only in the midrange. As this is a discussion forum so that others may understand the issue, the Acoustat 2's, a "full-range" electrostatic which were first introduced in 1980, have an efficiency of 85dB/watt/M. It would take a 100 watt signal to drive these speakers to 105dB, and since a tube amplifier typically has 2 dB peak headroom, the 60 watt tube amplifier can drive the Acoustat at some frequencies to exactly 105dB peaks. This of course, as with all tube amplifiers, with the inevitable high distortion, limited damping and bandwidth, noise, unreliability, inability to match impedence or drive reactive speakers, etc. The 105dB peaks at 20Hz and 20kHz with low distortion that a true "high fidelity" system SHOULD produce are just not possible with user35's system, and that is also a fact. As for testing, a square wave is much more revealing of sonic flaws such as bandwidth limiting or reaction to capacitance, and a spectrum analyzer would allow simple measurement of harmonic distortion and noise. However, the sound of user35's system obviously is his preference, and I certainly respect his right to love his system! But I digress, and to answer zkis' original question of "how much tube power is needed?" my answer is: NONE!!!

I recently heard a set of 93 dB Sound Dynamics RTS-P100s driven by a Rogue 88amp(60wpc/8ohms/120wpc/4ohms)Nearly knocked my eardrums in when I twisted the volume. I really agree- it is the first 3 volts that count.