Dummy load

[emperor_black]

If I get a cheap 8 ohm speaker, remove its cone so it makes no sound, can I use it as a dummy load for a tube amp?

 

[MrMarkIII]

If it's cheap, and therefore under-powered, it'll blow up, won't it?

 

[94Tremoverb]

Yes, and removing the cone - or even just blocking it up, I've seen people try this too - will greatly reduce the power handling because the voice coil can no longer cool itself properly. It will blow, and when it does your amp will go from load to no load at high power, which is about the worst thing you can do to it.

There is another way which will sound really weird but it *is* actually workable, if you either do the math or have a multimeter to check the resistance. Get an old electric heater - if you find a 1000W one, it will have a resistance of about 14 ohms. (Resistance = voltage squared divided by power, so at 120V a 1000W heater has a resistance of 120x120/1000 = 14.4 ohms.) This is actually about the right resistance to use for a 8-16 ohm dummy load - tube amps are not that fussy, and resistive loads are inherently less stressful anyway. Next, if the heater has a switch, it's best to bypass it so it doesn't accidentally get turned off - which will make it an open circuit, not good. Finally, cut off the AC wall plug and fit a 1/4" plug, and you're good to go.

I'm really not kidding, and there's no danger whatever of something like that blowing because even a 100W amp is putting only a fraction of the power it was designed for into it. Obviously if you find a 2000W appliance - it doesn't even have to be a heater, a kettle or some other electrical heating device will work just as well, provided you make sure it's permanently switched on - you can use that as a 4-8 ohm load. Check the resistance if you're unsure, to make sure you're in the right ballpark.

This isn't a joke, but make sure you know what you're doing! Running a tube amp with no load can fry it.

 

[emperor_black]

Wow, a Heater huh? That is indeed a radical idea.

 

[oyrgawd]

Resurrection...

Would this work to quiet my MKV speaker so I can connect the Slave out to my computer for quiet practice? Obviously I'd need to put a 1/4" plug on it...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=019-030&vReviewShow=1

 

[94Tremoverb]

Yes, it will work fine - but you might actually be better running it from the *4* ohm tap on the amp, even though it's an 8-ohm resistor. This is because the impedance of a real speaker rises with frequency and the average impedance of an "8 ohm" speaker is quite a bit higher than that. But, since Mesa amps are not very impedance-sensitive and purely resistive loads are less risky anyway, you could try it both ways and see which sounds the best, it won't do any harm.

You will also need some sort of speaker-emulator software in your computer or it will sound dreadful with the Slave output connected to it!

 

[oyrgawd]

Cool! Helluva lot cheaper than a Hot Plate.

I have Guitar Rig, and Reaper can probably do some IR magic...

Thanks.

 

[oyrgawd]

Ooh -- just remembered my RME Fireface has a speaker simulator onboard too. No CPU drain.