The dimmers were made by an a small company which are no more called PLS Lighting (I think). This was a one man band which meant the cost was extermely keen (about half of anything else available at the time). I think I bought them about 1988!! So with 4 shows a year and all tech rehearsals they are used about 40 times a year (640 times in total)
He decided however that he couldn't compete with Anytronics etc, so packed in. He has repaired one for me once (Thanks - I'd plugged a motor into the dimmer - didn't understand inductive loads etc then...), but the units are standard 5amp dimmers with no ability to change dimmer laws etc.
As they fail I will replace them, probably with Betapacks or similar, but they still work OK, and the fade characteristics were only noticed since we got a Fat Frog and a demux to run them. I guess this proves the issue IS the demux (Strand S72) but its not so bad, I hadn't noticed myself until a keen eyed operator pointed this out.
The things we amateurs have to put up with ehh?
SO I won't be killing the dimmers, we continue but start looking for replacement over the next few years