I wonder how linear it actually is...
I agree with Jeremy, a question mark for me as well.
With such high voltages, and being single ended, some problems come to mind.
1. The high voltages are typically 1,500 volts, give or take. Peak voltages of approximately 2,200 volts are possible, or more. With 2,000 volts, peak voltages in excess of 3,500 volts are possible, 2,500 volts, peak voltages in excess of 3,800 are possible. Of course, sufficient safety margin above the peak voltage is necessary for long life.
2. The insulation requirements are substantial, with accompanying problems to overcome. For instance, thicker insulation requirements of the output transformers (opt) increases the leakage inductance, thus lower high frequency response, unless special precautions are incorporated. I won't delve into such.
3. If designed with DC current flow through the primary winding, primary inductance is substantially reduced unless a larger core, or specialized core is incorporated. IN any case, complexity certainly increases.
4. If parafeed is used for zero DC current flow through the primary winding, then a proper high voltage capacitor with proper ufd value is necessary. Also, accurate reproduction capabilities is quite important as we added a part. (We already see strings discussing low voltage film capacitors.)
5. The power supply itself is tougher to design. This will require either series electrolytics, or high voltage oil types in parallel in order to increase the capacitance. A few ufd won't cut it for sufficient deep bass response.
One could purposely limit the low frequency response (a high pass design) and use a sub woofer/ss amp combination. That would allow for a higher frequency design of the OPT, which is good.
To give one a sense of how high frequency response affects lower frequencies, consider a -12/octave slope, which can occur (Slope of OPT depends upon Q at resonance.). If we design for
-3db at 40khz (I have seen such spec)
-2db occurs at ~31.5kc
-1db at ~20.5kc
-,5db at ~14.2kc
-,2db at ~7.2kc
Imo, it is much easier to design an SET using parallel tubes and lower voltages.
Cheers
steve