In response to firstname.lastname@example.org, 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!!!