This is one of our state-of-the-art hybrid power amplifiers that combines both the advantage of a transistor amp high current drive (tight bass and good speaker control) and single-ended vacuum tube amplification (warm and sweet sound with good depth, sound stage, and air).
The transistor output stage is a voltage to current converter circuit without any NFB or voltage gain, so the non-linear sound of transistors can be greatly eliminated. Left behind is the high damping factor that controls the speaker more efficiently. The tube section is working in an optomized single-ended operation mode to achieve the purest and most natural tonal quality.
If you were unaware of this amplifier construction, and you judged the sound quality by listening only, you would believe it was a pure tube power amplifier and not a hybrid.
The lower photo set shows a special version with a 5U4G tube rectifier and dual input level control, which is eminently suited for bi-amp applications.
(Additional cost applied)