Being that I am not a tube-audio fanatic or someone that knows entirely about them, I cannot say with complete certainty that tube-amps will remain safe while using this particular selector switch.
What I can offer, is that there is a 12 ohm resistor and 0.047uF cap terminating the speaker-level input to this switch at all times. This is present even to the input side of the fuse in the case that the fuse might blow under higher power output to protect the speakers, while that CR load prevents oscillation. This particular CR filter might not be enough to sustain the tube amp's happiness or normal operation as it's in a very high frequency bandwidth. I don't know the bandwidth that is requiring a load on a transformer coupled outputs, so I cannot understand what it would require. Under switching, the avalanche MOVs are across the outputs, so that they will take the problems on that side if arcing were to occur. Switching under higher power should be avoided if at all possible, but I included parts to try and remedy what could happen if this did in fact occur and a result was problematic.
Later,
Wolf
What I can offer, is that there is a 12 ohm resistor and 0.047uF cap terminating the speaker-level input to this switch at all times. This is present even to the input side of the fuse in the case that the fuse might blow under higher power output to protect the speakers, while that CR load prevents oscillation. This particular CR filter might not be enough to sustain the tube amp's happiness or normal operation as it's in a very high frequency bandwidth. I don't know the bandwidth that is requiring a load on a transformer coupled outputs, so I cannot understand what it would require. Under switching, the avalanche MOVs are across the outputs, so that they will take the problems on that side if arcing were to occur. Switching under higher power should be avoided if at all possible, but I included parts to try and remedy what could happen if this did in fact occur and a result was problematic.
Later,
Wolf