I had these on a station I engineeered. They were dreadfully noisy, even by the standards of the mid-70s, and they had quite nasty and obvious distortion on peaks. I was so frustrated by them that I designed and built my own limiters, which we installed late at night to avoid the ire of the managers, and evade the senior engineer. In the following days, many listeners and staff commented on how much better the station sounded!

I found one of the prototypes when I cleared out some of my old gear. It still worked, which was a pleasant surprise. More recently, I’ve been designing much more modern designs (though staying in the analogue domain), and now use only PWM for voltage-controlled attenuation. It confers a number of advantages, including easy channel matching, low distortion and no noise.

Haven’t things moved on over the last fifty years?

If I recall correctly those Collins 26U-3 and 26J-3 are based on the 741 op amp, and compression is simple manipulation of the feedback path around the 741. I’ve never seen either one show up for sale….not that I would look either.