Watch Vintage King restore a Fairchild 670. What is  a Fairchild 670? Here’s more from Universal Audio WebZine:

…the stereo Fairchild 670 is probably the “Holy Grail” of compressors in studio gear esoterica, not only because of its price but its extreme rareness and the difficulties in maintaining such a piece. The 670 can get fetch $30,000 and beyond on the vintage market. With its 14 transformers, 20 vacuum tubes, and 6 rack-space encompassing girth, the Fairchild 670 is the heavyweight champion of compression, weighing in at 65 lbs.

Originating from the early 1950’s, the design of the 670 uses a single push-pull stage of amplification with an extremely high control voltage. The Fairchild 670 is a variable-mu tube limiter. Variable-mu limiters are unique in that they use tubes for gain reduction, and not just as amplifiers. The audio path is quite simple, and compression happens directly in the audio path, rather than sending out to a separate compression circuit.

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