Then put 100 ohm resistor from pin #9 to pin #7?
If this is correct then to add a ultralinear to triode switch you would.
Remove green or green white wire from pin#9 of each tube and solder to separate poles of DPDT switch on the same end.
Solder wire from pin #9 to center pole of DPDT switch.
Solder 100 ohm from pin #7 to DPDT switch opposite end from green or green white wire.
All wiring to and from switch side must be to same tube.
Also I once had a MKIV which I triode, did not work. Was wired correct. Asked a guy about it, he thought it may be osculating at radio frequency, suggested 220 ohms. It worked fine. Is this common?