The Federal AM-864/U is an all-tube audio limiting amplifier originally made for the US Army in the '40s and '50s for use in AM radio broadcasting. It has since found use in recording and mixing studios for its unique sonic texture.
The Federal is a quite fast limiter, it has a great midrange but also sounds a bit gritty. Works great as a parallel compressor on vocals, to make a bass guitar more punchy and on guitar amps (especially in combination with a Royer 121).
The Gear Rack