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Ceko

Dummy load on Tube Amp

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Hi there I have this new Tube amp that I bought just as a headphone amp but I’m now under the impression that the speaker bindposts need a constant load. I understand I can use a dummy load but can someone please explain what that means and what I need for that. 
 

Is it just a little resistor or something? What kind do I need? My little amp is just 3Watts per channel on 8 ohms...

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1 hour ago, Ceko said:

Hi there I have this new Tube amp that I bought just as a headphone amp but I’m now under the impression that the speaker bindposts need a constant load. I understand I can use a dummy load but can someone please explain what that means and what I need for that. 
 

Is it just a little resistor or something? What kind do I need? My little amp is just 3Watts per channel on 8 ohms...

10ohm / 10 watt power rated wire wound resistors, one for each channel.  Used to use them as dummy loads when doing tests on Amps, using a signal generator and an oscilloscope.  If you can find ones with a bigger power rating, they would be even better.  A slight word of caution!  They are likely to get a bit warm.  

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It would be strange if the amp didn't have a headphone socket that disconnects the speakers when a headphone is being used. So saying Ron is on the money in the post above. Don't get a 3W rated resistor as it will get fiercely hot, I'd prefer a 25W wire wound myself, but don't sweat it.

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Sooooo should I or shouldn’t I use it? The speakers are in fact disconnected when I use the headphone.

The manual says: forbidden to operate as unloaded. Maybe that means it needs a pair of headphones when it’s operating in headphone mode.

Edited by Ceko

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I'd play safe and put a dummy load resistor across the speaker terminals. Valve amps (certainly valve amps with output transformers) should never be run without a load, as you can fry output transformers. About the most expensive part of the amp. I would expect the entire output section to be killed when using headphones, but for the sake of a couple of resistors, there's nothing to lose.

I use some whacking great old wirewounds rated at something obscene for testing, but that's because some of my oddments are a touch more than 3 watts. For a 3W output, I'd side with James and just get a couple of 25 watt ones. They will run less hot.

In headphone mode, don't run it without phones connected. Though presumably the switch from one to t'other is done by plugging headphones in anyway.

Edited by rabski

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If I search for those 25 Watt resistors I get all kinds of ohms I can choose. Does that matter anything? Or just go with 8 ohms just like the speaker?

By the way @rabski the amp does have a switch to choose for speakers / headphones :-) So it’s not automatically selected. The model is a Line Magnetic mini 84.

Edited by Ceko

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I just had a discussion with my dealer. He agrees that if I switch to headphone mode, the speaker terminals give no sound, so there's no need to add a load.

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