Inchwarm54.
My CX3 has the power master circuitry. It makes me dig,in all metal anyway.
My treasure hound box coil came with the CX Plus when I bought it new in 2010.
The GTAx's don't work , I guess the coil plug is different.
As for your older machines. Do a search on the net for "Vintage Metal Detectors".
You will find many pages of info and a few forums dedicated to the Vintage machines.
Where I'm at an older timer cleans up the beach daily. Even tried to run me off the public beach claiming its his.lol. I got my permit. I'm hoping this 10×14 coil in all metal will do the trick. I've run an Explorer XS and a MXT here,pulled some older nickles from a deep cut near the shore. Which means he has'nt gotten it all,its just Deeper. This beach and port date to the 1700's,so there has to be some good stuff left. Seriously this guy has the beach so clean I can hardly find an old pull tab.lol.
If I can ever get my Sovereign GT back from my lil brother in Alaska I could go very deep in deed.
Welp hope I helped ya a lil more. Did you inherit these machines?
T. M.