Speaker Switch That Protects Tube Amplifier

It's actually very simple, just have a load resistor, of sufficient wattage, subbed for the speakers when you flip the switch. That way the amps can always see a load when they are not attched to the speakers and there is no chance for accidents happening.

As far as the source goes, you should have a look at the output impedance of the source and the input impedance of the paralleled amp inputs. If it is 10-20X you should be good to go. If not, all is not lost, you can use an output buffer at the output of the source and this should present a high impedance to the source and a sufficiently low output impedance to easily drive the paralleled inputs of the two amps.

Keep in mind that, with some amps, when they are turned off, the input impedance is significantly lowered, so I would do my experiment with one amp off to see if you need the output buffer or not. But they are cheap and fairly transparent so you should have no issues.

You are more than safe with a 100W resistor. Since you usually, probably, only play music at a few watts you may very well be able to use a resistor of much lower rated wattage.

Your friend is the EE!

If I were doing it, I would use a make and then break switch that would put the two loads in parallel and use a load resistor of much higher impedance then you are using so that in parallel with the speaker load it would still be within the acceptable load range for the amp.

Al if one uses a break them make switch would the amp not see a load for a moment as it is switched😢?

Beautiful, Al thank you for taking the time to educate me on that point. I appreciate it. Have a good holiday weekend.