parallel single ended half power mod

[mooreamps]

Removing the B+ from the screen and grounding the screen (with no B+ supplied) should be OK, but that isn't quite what Gary said.
Here is what was written so as not to confuse anyone:
"Well, the way I would do it, connect the screen to a toggle switch. Toggle the screen to ground to disable",

I was just pointing out that the B+ screen supply, grounded with the screen, could lead to a minor catastrophe and shut the entire B+ supply off to the rest of the preamp... even if it didn't blow something up.
I guess you could use a SPDT with the screen connected in the switch's middle lug, B+ on one end and ground the other or a DPDT switch where one side removes B+ and the other grounds the screen if needed...etc.
Still you'd need to address the unloading of the B+ rail and the impedance mismatch of the single power tube.
Neither of those two problems would be a big issue though.

yes, that was the intent. Sorry I did not make that more clear.

-g