Speaker Switch That Protects Tube Amplifier

Marty, note this statement in one of Mceljo's earlier posts:

To bridge the instant between the speakers and the dummy load resistor on the tube amplifier we will also add 150 ohm 5W or 10W resistors on each channel based on the recommendation from the Niles manual that was linked.

And in his most recent post:

The revised plan is to use the dummy load resistor (a parts express item) on both inputs and also put 150 ohm resistors on both inputs to make it a fail safe design for a tube amplifier.

So as I understand the plan neither amp will ever see a load that is lighter than 150 ohms, even for an instant. That seems reasonable to me, although I suppose it would be good practice to not throw the switch when music is playing (since the possibility of damage resulting from having a load that is too light is very small if no signal is present).

Best regards,
-- Al

My current solution is to have two sets of cables at my speakers that I manually switch depending on the amplifier that I want to use. To this point the tube amplifier has always been shut off (though not always at room temperature) before disconnecting the speakers. The receiver has been used to pass the audio to the TV via HDMI without the speakers connected many times.

My ultimate goal from a fun perspective is to be able to do live A/B switching as any other delay makes it virtually impossible to accurately "remember" what it sound like for comparison. It will likely be a gimmick type of event at first that eventually becomes rare. I

The long-term improvement from a practical standpoint will be that I can have the tube amplifier on for listening, switch to the receiver for watching something with my wife, and then go directly back to the tube amplifier without having to turn it off. As a general rule I don't turn the amp back on until it's cool and because the sound is much better with everything warmed up short power cycled listening just isn't the same.

To be able to do live A/B switching, this is an idea:
A Shorting Contact Style 3 Deck 3 Position Rotary Switch,
Deck 1: pole connect to speaker +, position A to AVR + output, position B open, position C to Tube Amp + output
Deck 2: pole connect to speaker -, position A to AVR - output, position B open, position C to Tube Amp - output
Deck 3: pole connect to 8ohm 100w Dummy Load Resistor to Tube Amp - output, position A & B jumpered and connect to Tube Amp + output, position C open
Hope this help

VERY clever idea from Imhififan. Kudos!

To be sure it's clear, I would reword the description of the Deck 3 connections as follows:

Deck 3: pole connect to 8ohm 100w Dummy Load Resistor; other side of that resistor to Tube Amp - output; position A & B jumpered and connected to Tube Amp + output; position C open.

Also, if this approach is pursued it might be desirable to use something like a 16 ohm 50W resistor, or even a 32 ohm 25W resistor, rather than an 8 ohm 100W resistor. The reason being that when the switch is thrown between positions B and C there will be a brief instant when the tube amp will see the loading of both the speaker and the resistor. That may not be a problem anyway, but I can envision the possibility of a significant thump occurring with an 8 ohm resistor, especially if the amp uses feedback.

Also, Mceljo, as opposed to the approach you described earlier, with this approach you would of course have to provide markings or some other means of identifying which specific terminals each specific amp should be connected to.

Marty (Viridian), thanks for the nice words and the good wishes, which I reciprocate.

Best regards,
-- Al