05-24-13: MapmanInterestingly, as far as I am aware he was also the only manufacturer of consumer-oriented audio power amplifiers utilizing the 300B directly heated triode power tube, between the earliest days of hifi and the resurgence of interest in that tube that occurred in the last three decades or so.
... I believe Lincoln Walsh used his engineering experience with radar systems in WW2 to get dynamic speakers right while the rest of the world missed the boat. Pretty radical.
Also, some of his amplifiers used 2A3 DHT power tubes, and similar comments apply to them, with the slight qualification that his use of 2A3s was preceded by their use in the power amplifier sections of certain high end radios of the 1930s.
Those Brook Electronics Company amplifiers are highly collectable these days, and go for big $$$ on the rare occasions when they appear for sale.
Best,
-- Al