Tube Amp on without speakers connected?

[pstrisik]

Hi All,

I'm trying to set up a configuration where I have a two channel tube system integrated with my home theater system. Without getting into all of the complexity, basically I'm having a Pr17LS pre into a Pr11A amp for two channel. I have an Onkyo pre/pro into Class D solid state amps. I want to run with a single set of main L/R speakers. I have a switch to accomplish this. Problem is, I would like the tubes to stay on at times when I will be listening to music after our movie so they will be warmed up and ready. When watching the movie, the switch would disconnect the speakers from the 11A.

Is this a risky proposition? The maker of the Class D amps says no problem, but I think I've heard that it can be a problem with tube amps.

Thank you for your insights........ Peter

[admin]

I have to tell you that I have never tried running my amp without speakers connected, so I can't speak from personal experience. From what I have read some people say, "no problem", others advise against it. I can't find any reference to running my amp without load (speakers) in my CJ Evolution 2000 manual.

I did find this thread that you may want to read: AudioKarma.org Home Audio Stereo Discussion Forums > Tube Audio
Tube amp with no load

From the readings it seems like you are taking a risk. How much time does it take for your tubes to warm up? You probably don't want to run the tubes every time for 2 hours while watching a movie, just for 45 minutes of listening? If you don't want the warm up time and do not want to leave the amp unloaded, you may be able to connect some cheap speakers to the amp to run in parallel that you can disconnect once your regular speakers are connected up again. This way the amp is always loaded. Once again, I have never tried it, but it may work and be safer.

Whatever you decide to do, I would be a little cautious as you don't want to damage your amp for the sake of a 3 minute warm up time,... IMHO.

[pstrisik]

I think I'm going to go with not warming up the amp. The alternatives are to use the tube amp for everything replacing tubes more often (and possibly shortening the life of the amp), to run with a second set of speakers or to do a lot of manual connection/disconnection.

CJ support (anonymously by email as Ed is gone) advised against it. I found through internet research that Cary's design allows this, but most others don't, including CJ.

This is still in anticipation. I'm expecting a Pr17LS in the mail today!

.......Peter

[billyz]

You should not run a tube power amp with out a load. If you want disconnect the speakers and leave the amp on you should have 180-200 ohm , 20 + Watt Resistor across the + and - speaker terminals. you can leave it in place even while the speakers are connected. It will Protect the power tubes from arcing .

[pstrisik]

Interesting. No effect on the sound when you leave them on? I would think it would increase the load.

.......Peter

[foothillphile]

My 2 cents; As I recall it, the output xfmr is the problem, and yes cary audio has a solution, better voltage insulation on the

primary windings.

The problem comes when the secondary has no load and that looks like an infinite load to the xfmr. A xfmr secondary reflects

back to the primary whatever it sees, but then you have to consider the turns ratio; high impedence primary and low

impedence secondary (typically 8 ohms) makes things worse. The output tube(s) sees the primary as it's load, so when a

reflected load of infinity times the turns ratio comes back and the tube sees such a high impedence load, it swings it's intire

voltage accross the primary windings and the insulation isn't made to handle the intire voltage, and the windings begin to short

between each other. Cary Audio fixed this, but many amps will still fail this way, and it requires replacement of the output

xmrs.

Now this reflection will only occur in the presence of an audio signal (AC), DC will not reflect anything. So if you're planning to

run a signal into this amp without a load while watching video... not good!

Good luck.

[jzaret]

I am going to add something that may or not be popular with this thinking. First of all, I would not run an amp without a load because it was designed to have one when operating unless you are repairing it or taking measurements. I know a of people put CD in constant play to get to the magical number of hours. My thought on all of this is kind of two fold, first how will you know it has improved and when. There is no exact magical number of hours, they are estimates, on when "things" break in. IT is somewhat of a "ladder" affect. "Things" get better in intervals not all at once. I refer to "things" as tubes, caps and other parts which may need a break in period. My second part is why not enjoy the ride along the way.

One is basically missing out on the enjoyment of the amp or whatever was purchased. When doing it this way you will know when things "get better or open up". I usually say that when it does happen it seems like a vail has been lifted off and another layer is discovered or is clearer and cleaner. Why waste time enjoy your equipment now.
Just my two cents.

Jeff

[pstrisik]

I am going to add something that may or not be popular with this thinking. First of all, I would not run an amp without a load because it was designed to have one when operating unless you are repairing it or taking measurements. I know a of people put CD in constant play to get to the magical number of hours. My thought on all of this is kind of two fold, first how will you know it has improved and when. There is no exact magical number of hours, they are estimates, on when "things" break in. IT is somewhat of a "ladder" affect. "Things" get better in intervals not all at once. I refer to "things" as tubes, caps and other parts which may need a break in period. My second part is why not enjoy the ride along the way.

One is basically missing out on the enjoyment of the amp or whatever was purchased. When doing it this way you will know when things "get better or open up". I usually say that when it does happen it seems like a vail has been lifted off and another layer is discovered or is clearer and cleaner. Why waste time enjoy your equipment now.
Just my two cents.

Jeff

Update:

I've succeeded in getting a Niles automated speaker switch to work (SPK-1). Basically, I have speaker outputs from both amps going to the switch and cables from the switch to the speakers. There is an AC/DC adapter that runs to the switch. When the switch detects any power from the adapter, it switches to the other amp. When the power to the switch is off, it switches back to the default amp. So, when I turn on the tube amp, the switch connects the speakers to it automatically.

This means no warm up time for the tubes, but the convenience outweighs the bit of time of listening before it is running warm.

Jeff, Break-in has not been an issue in this thread. I may start another thread about break in regarding a preamp.......

[admin]

Interesting setup, I have never heard anybody do this before. Any chance you can post a picture, I would just like to see how you have the entire thing hooked up. Sounds cool!

[pstrisik]

Interesting setup, I have never heard anybody do this before. Any chance you can post a picture, I would just like to see how you have the entire thing hooked up. Sounds cool!

Thanks and sure, I'll post photos once I bring the 17LS back up stairs in a couple of weeks (running 12 hours/day or so). I'm overdue for posting to the gallery as well. Waiting for my system to hit a stable point before I do - like waiting for Godot! Seriously, restored speakers went in a few weeks ago, breaking in the pre. Just tested the Niles switch last week. So it will hit a (relatively) stable point with the pre integrated. Enough for photos anyway! But a diagram may be more decipherable. I'll see about both.