by EWBrown » Fri Dec 08, 2006 8:20 am
As long as the switch can handle at least 450VDC (breakdown voltage) between the contacts and the switch's body and mounting, this should work fine.
The actual DC voltage potential difference between the contacts for each pole will be fairly low, presuming "common" to the G2, and the other contacts to plate and SG tap on the output transformer.
The main thing to remember -even though you have stated thos before, is to avoid flipping the switch when the amp is powered on.
If you can locate a decent three-position, four-pole switch, then the choices can be Pentode mode, UL mode , or Triode mode. This starts go get a bit complicated, but should be feasable.
VTL (Vacuum Tube Logic) uses this same approach on many of their amps, I've seen it done with their MB450s (which use 8 6550s or KT88s in PPP). There is around 600VDC pplate voltage, and they use what looks like a fairly cheap plastic body and "bat handle" DPDT switch for each monoblock.
Another VTL PPP amp (with 4 6550 / KT88s per channel) uses two switches per channel, in what they call a "tri-tet" mode. With this arrangement , one pair of the tubes can be run UL, the other pair can be run Triode, at the same time, on each channel. THis gives three choices, all truode, all UL, or half and half.
Locating your 4PDT switch between the bias pots would be a good choice, or perhaps on the back of the chassis.
/ed B in NH
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