I had the fortune to repair one of these valve compressors recently. Two 12AU7 valves, optical coupling, built to the standard of a battlefield weapons system. I was expecting it to sound good. Some compressors just seem to be so subtle that you sometimes don’t even notice them. Not so with the squeezebox in extreme settings the squish gets so much that bass takes on a percussive tone.
If you need a repair of one of these, get in touch as I do mail order repairs on small units like this that can be sent in.