The F2 is a stereo power amplifier which offer 5 watts output. Like the F1, it is a current source, but it is different in several ways. The F1 operates in what I would call “balanced single-ended Class A” and the F2 operates as simple single-ended Class A. The output impedance of the F1 is 80 ohms, but I have provided the F2 with an output impedance of 15 ohms, based on the observation that no useful application of the F1 called for a higher figure. As a single-stage single-ended circuit the F2 has no use for balanced input connectors so it simply has RCA inputs, as seen here in this simplified schematic:
While the F1 has a crisp sounding 3rd harmonic signature, the F2 has a richer pure 2nd harmonic character, and this difference is the primary justification for offering a second no-feedback current source amplifier.
Another remarkable thing about the F2 is the very wide bandwidth – it is down about 0.5 dB at 200 Khz.
Will it replace your favorite 300B SET? Maybe, maybe not. In any case the only copies are available used. For a short time there are a very few F1J units available which use new power Jfets instead of the Mosfets – see the F2J product page.