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Can a tube amp be damaged by a speaker switch?

Help please from the tech crowd.

I had a room with two systems....one for audio and one for TV. The audio is a Leben tube amp into Altec Valencia speakers. The TV is a Marantz receiver into a group of five budget small speakers. My goal was to use just the Valencia's for both amps because the big Altec's are so much easier to hear dialogue on the tv. I also want to clear up wire clutter in a cramped cabinet. 

My solution was a Luxman AS-55 speaker switch which a very high quality unit designed to allow 3 speakers and one amp, or in reverse setup, three amps and one set of speakers. During set up, I had a question and called the Luxman US manager who picked up the call and was so gracious with his expertise. Great service. The problem is after hearing my questions he said..." we do not recommend using a switch with a tube amp as running tubes without a load can damage the amp...even break it. 

I can use the switch if the the tube amp is turned on only when running into the speakers. The problem with that is the Leben really needs a good half hour to warm up and I would like to do that while watching tv. It will make it cumbersome to switch back and forth between the two. 

Eliminating the Luxman AS-55 switch and just using two sets of speaker wires is an option, but I really do not want to have to plug and unplug the bananas on my Audience cables as that can only hurt them and its a hassle. Im also worried about potential damage to the Altec's with two amps hooked up. 

My question is for the experienced tube users. How much risk am I running if I use the Luxman switch as I intended? Can it really damage the amp or is the Luxman rep exageratting the risk for laibility reasons. What is the potential damage?

 

128x128tamarack4
carlsbad2's avatar
carlsbad2
1,623 posts
 

If you turn your tube amp off before switching, no problem.  

Jerry

imhififan's avatar
imhififan
2,204 posts
 

I actually have a Leben and during the course of modding it, one night I accidentally left the dummy load off and ran pink noise. Next morning..I freaked out...yet, no problem with it at all.

Many commercial tube amp can survive without load connected if not driven into clipping. However, a general rule of thumb is to always load a tube amp while running to prevent potential damage.

 

 

technomagus
13 posts
 

Depends on the amp: anything made by Octave for instance wouldn’t matter at all. Others I know to be less robust 

imhififan's avatar
imhififan
2,204 posts
 

The Octave Audio amplifier is not a traditional tube amplifier design, it uses protection circuitry to protect its output from low impedance or short circuits, eliminates multi-tap speaker terminals, and behaves more like a solid state amplifier than a tube amplifier!

tubehead120's avatar
tubehead120
35 posts
 

I have had transformer damage from the flyback effect years ago when I first started building tube amps and used a switch to compare them.

From an engineering standpoint, paralleling a load (the speaker) with a resistor 10x or greater will have no practical effect on the signal received by the load (and it will draw an insignificant amount of power).

For my hifi amps I parallel the entire secondary of each channel (using the highest ohm taps) with a 200 ohm 5 watt Kiwame carbon film resistor (I just connect it through the holes in the binding posts on the amp).  I have never been able to hear any difference, and neither have my friends.

For my guitar amps I use the same values but cheaper carbon film resistors.

I've never blown up another amp and I've done a lot of switching.

 

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