David Berning Quadrature Z as new "mint"

[email protected] with questions.
If you know these amp at all you know they are very very special.
Both single and balanced input, all balanced amplification.
Special triode-like screen-drive output stage.
Low negative feedback, no phase compensation used.
Constant output impedance over entire audio spectrum.
Built-in five-stage power-line filter and surge suppressor.
Non-magnetic chassis prevents skin-effect induced distortion.
Separate shielded enclosure for power supply reduces noise.
Power consumption: idle-125 W; max-500 W. Power factor corrected.
Line voltage required: 100-260 VAC, 50-440 Hz.
Signal to noise: broadband (typical) 55 dB, all feedback settings. 20 kHz bandwidth (typical): 98 dB, NORM feedback; 92 dB, MED feedback; 86 dB, LOW feedback. All figures unweighted.
Distortion (typical, at 8 ohm loads at 200 W): 0.3%, NORM feedback; 0.5%, MED feedback; 1%, LOW feedback. These double at 4 ohms.
Typical output power at onset of clipping: 8 ohms 220 W; 4 ohms 270W.
Frequency response at 5 W, 8 ohms; +0, -3 dB: 2 Hz to 90 kHz, NORM feedback; 2 Hz to 60 kHz, MED feedback; 2 Hz to 40 kHz, LOW feedback.
Frequency response at 5 W, 4 ohms; +0, -3 dB: 2 Hz to 50 kHz, NORM feedback; 2 Hz to 40 kHz, MED feedback; 2 Hz to 30 kHz, LOW feedback.
Full power bandwidth (-3 dB), 4 ohms: 20 Hz to 50 kHz, NORM feedback; 20 Hz to 36 kHz, LOW feedback. Low frequency bandwidth limit intentionally set by speaker protection (0dB down at 20 Hz).
Typical output impedance (measured at 1 amp, 60 Hz): 0.8 ohms, NORM feedback; 2 ohms, MED feedback; 5 ohms, LOW feedback.
Sensitivity, 200 W, 8 ohms: 1V, single-ended input. Feedback gain compensated.
Input impedance: 35 k -50 k, depending on feedback setting, both single-ended and balanced inputs.
Tube complement: (4) 33JV6 output; (2) 16GK6 driver; (3) 12AT7 input and gain.
Size: 48 cm wide, 48 cm deep, 20 cm high, (19 X 19 X 8 inches), including connectors and feet.
Net weight: 15 kg (32 lb); Boxed, 17 kg (38 lb).
Finish: silver face and back anodized aluminum; top and sides: light gray paint with silver anodized accent bars. Also available in black anodized aluminum by special order.
Comes equipped with Stillpoints TM isolation feet.