Q./   How is a triode/pentode switch best implemented on a 6v6?
 
A/.    Easy- just use a SPDT switch. Connect the common to the screen,
 the NC contact to the normal screen supply, and the NO contact to
 the plate. Note: when you flip it the screen supply will be briefy cut, causing
 a pop in the speaker. To eliminate this, use a make-before-break
 switch. Klunk-klick every trip!


Given that power supply mods are not a good hum
removal solution in tweed type circuits, filament hum
balance might be a really good thing 
 
jsn



Having said that, though, I think you might be
overestimating the role of hum from the heaters. It's
really only an issue in high-gain rigs like Boogies,
5150s, and phono preamps. The Champ circuit is not
high-gain, but it IS very sensitive to hum on the output
stage B+, especially in triode mode. So I think your
efforts would be better spent getting a well-filtered B+.
Why not put a big choke in and take your output stage
B+ off the second filter cap, after the choke. (Who said
power supply mods were no good?)