I tried to explain that above. In three of my amps C216C is connected to V203, represented by the line "X". Alternatively, in one of the amps C216C is connected to v204 represented by the dotted line "Y", which would be in place of "X" in that amp.
Thanks for the note on "electronically the same", that goes to the root of my question and what I am trying to learn here and in general. I will re-wire according to your diagram.
That makes more sense to learn some amps, like these film projector amps, would be designed like this with screens higher than plates, and to learn how to fix it for guitar.
My 5w 30v zener diodes should arrive mid-week. Where in the diagram do I insert it?
Trying to follow your diagram about dropping B+ on an 18w, it looks like the end with voltage stripes connected directly to C216A, the other end going to R228?
Then do I leave the current OT wiring in place? The OT currently goes to the first 6x4, then one wire goes to C216A, and another wire connects to the other 6x4? I imagine I just shift the connection at C216A over to be at the other end of the diode.