Can a tube amp be damaged by a speaker switch?

tamarack4

... we do not recommend using a switch with a tube amp as running tubes without a load can damage the amp...even break it ...

Absolutely true.

Running a tube amp with no signal into the amp, and hence, no output, should not be a problem.  But, it is too easy to accidentally have the amp amplifying without a load.  One thing you could do is install a dummy resistor to act as the load when the box is switched to play a non-existent speaker.  just google 8 ohm dummy load and you should be able to buy the right set up (dummy resistor plus a suitable heatsink).

What is the potential damage?

If the load accidentally disconnected from the tube amp while playing, The inductance of the output transformer will produce a large fly-back voltage, this is lethal for components in the amp, it can damage the output tube or will arc across the output transformer primary winding and burn it up.

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.

What a wealth of knowledge this group is. It sounds like there is no quick and easy solution, but there are options. I'll try to digest this and run your suggestion by my audio repair friend.

Thanks so much.

This is amplifier dependent. Almost all solid state amplifiers are stable into no load, but not all tube amps were.

Check with the vendor.

In _all_ cases you must ensure that the switches used are "break before make." That is, they open completely before making the next connection. The alternative, make before break, can be disastrous for any amplifier.

If you are confidant that you can properly use the correct switch consistently (and you will not have others using the setup) then go for it.

If a speaker becomes disconnected (cat/dog/ferret whatever) while playing music and it's not noticed you have the same damaging scenario - stuff happens.

DeKay

Buy a modern solid state amp with protection.

I share 1 pair of speakers with 2 amps. I always forget to switch until no skun emerges. I’ve never hurt nothin’.

What you are attempting sounds hazardous to your HiFi budget.

The knowledge and expertise shown by the members of this Forum never ceases to amaze me!  I have no doubt that if added up, the years of experience in this group of Audiogon Members, as a collective, would total in the thousands.

Sure, at times there is the very rare member that can be an utterly complete asshat -- but in my years of lurking in the shadows and observing I can honestly say those members are pretty rare.  When they do show up, the Group as a whole is pretty quick at policing their own.  I've learned more about this hobby in the last 7 years from you men and women than I had absorbed in my previous 55 years roaming this Earth.  A heartfelt thanks for not making me feel like a complete idiot when I've asked the occasional question.

"What's so funny about Peace, Love, and Understanding?"

I am a bit confused. All of the comments are good, and are good suggestions for what you are choosing for a solution, but I think the approach is all wrong.

What Marantz receiver are you using? Does it not have Pre outs?

What Leben amp? Is it an integrated or pure amp with a pre in front of it?

I would look for ways to have the Marantz feed into the pre that drives the Leben amp or the Leben integrated and the Altec Valencia speakers as the Front L and R for theater, and solve the problem that way. Much better and safer unless the issue is that you spend much more time in theater mode, and do not want to put that run time on the Leben tubes. If you like the Altecs for speech and for your 2 channel, that would seem to be the best choice. Balancing levels when in theater mode may take a little work, but should be doable. Add an additional unity gain pre if you need more inputs for the Leben  - Altec Valencia chain.

as budjoe mentioned, and why he asked for your system specifics:

Front Pre-outs is a definite solution, some receivers have pre-outs, but not Front Pre-Outs, some do, it’s an important feature.

IF Front Pre-Outs: you would be using your Marantz to power center and surround speakers only, and the front pre-out would go to your Leben Tube amp, which would ALWAYS power the front speakers, music or video.

The Marantz would control the volume of all, including the volume of the front pre-out, and any settings you change in the Marantz would be passed to the front pre-out.

NEXT: We need to know the model # of your Leben, and if not an Integrated, any pre-amp in-line, and it would be good to know what other 2 channel sources you use the Leben for.

Modern preamps have HT bypass, simply a selectable preamp input (for Video) that bypasses the pre-amp’s volume control (so Marantz can control the volume along with the other speakers the Marantz is powering.

Older equipment, no HT Bypass: knowing it’s specifics, a solution can be found.

I use a tube amp and a solid state amp and share one pair of speakers with them. I am using a Solupeak P3 switcher. I've been using it for a while now with no issues. I just make sure I am extra careful to make sure the switcher is set for tube amp before powering on my tube amp and making sure the other amp is off. One time I powered on my tube amp without switching the switcher to it (so no load) but then powered off the tube amp right after since I forgot to switch the switcher. It didn't cause any issue, but maybe I got lucky. Realize this is a risky setup with my expensive tube amp. But the convenience is great. I also always have the volume knob all the way down when turning on tube amp and never have any source playing.

Why don't you just get a proper centre channel speaker?

In a 5.1 HT system the fronts don't carry the dialogue anyway.

@imhififan 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.

​​​​​​​I know there are vintage guitar amps that have blown up from not having a load, and I dont know the technical reason, but it doesn't always cause problems.

We are warned about the practice, and it is good advice not to do it, but I have not heard of actual failure.

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

Jerry

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.

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

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!

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.

This is what I use in a same setup. It has built-in load resistors.

NEOHIPO ET30 Amplifier Speaker Switcher, 2-in-2 Out Dual Analog VU Meter, Audio Switcher with DB Panel Display https://a.co/d/7cHGifD