DeHavilland is a Washington state based maker of true Class-A, single ended triode (SET) tube power amps such as the 50A. They've been in business since 1997, and have a claimed mission of building the "ultimate vacuum tube amplifiers." They also make preamplifiers.
Notable deHavilland products include:
deHavilland 50A, rated at 45 watts per channel
deHavilland GM70, class A, rated at 40 watts per channel