And believe me, it 'sounds'.
Has the opportunity to work 'bridged', means 500W (!) mono. This should be enough for most subwoofers (I used it fullrange).
A classic Bob Carver design from the beginning of the 80's. As the name implies, it uses Bob Carver's magnetic field circuit, which means it's got three voltage rails and a commutator circuit, making it possible that such a small device has a lot of power and no heat-sinks at all.
I 'tuned' mine with a power-switch at the back of the device (on the pics next to the fuse). A real downside are the flimsy output-clamps, making it impossible to use speaker-cable with a serious diameter. I bought four high-quality banana-sockets, but you have to disassemble the whole amp to change them.
Nevertheless a real eyecatcher.
Still try to exchange the output-connectors for serious ones.
A nightmare for each and every tube-fanatic ;-)
Scanned manual of the M-400 is now available (yes, page two is missing... sorry) here.