I might have a switch for you. I have a 1977 Doctor Q that I’ve been tinkering with (the decay is warbly) — I haven’t yet tried the switch, but if that’s the problem, I will replace it and you can have the original. A year or so ago, I got some pretty helpful answers about a 1981 Mini-Chorus (not Full Chorus) somewhere in these forums, so I’m glad to have a chance to help someone else out.