The project is a single-ended medium power tube / solid state hybrid amplifier delivering something above 25W RMS into 4Ohm speakers and can be driven directly from a CD player (if that is a preferred option). Input tube is an actively loaded 6SN7. The power stage comprises a KT66 cathode follower driving a 2SC5200 power BJT which is cascoded by an IXFN32N120 industrial power MosFet. The output signal at the MosFet's drain is fed back into the screen grid of the KT66. This makes the tetrode virtually a very low µ triode. Output transformer is a Lundahl LL1693(230mA) for SE operation.The amps went into operation on April 12th 2017 and since then run without any problems. I am truly happy with their performance. Instruments and voices are natural and detailed and seemingly independent from the speakers. I do not own high efficiency speakers but run my amps with two Newtronics Temperances speakers. Although the measured output power is little above 25W per channel I can hear music very loud. Of course my statements are subjectively biased. However, I do not regret one single Euro I put into this project, not counting the challenge and fun to design and build it. The full article describes the concept, the circuit and the power supply in detail.
Impressions from Nashville, Tennessee in March 2018
super triode, vinyl, audio, analog, single ended, SE, power amplifier, hybrid, tube, KT66, 6SN7, ECC88, Mosfet, Lundahl, MC phono stage, preamplifier, MM, MC, moving coil, moving magnet, LL1693, LL1667, LL9226, LL1933, RIAA, folded cascode, 2CS5200, MAT12, 2N3810, LL1660S, IXFN32N120P, balancing amplifier