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Dummy load and power amp for tube amp?

M

mr_goodbomb

Oct 10, 2009
270
1
#1
I have a Sunn 200S for bass. It sounds great, but I have to crank it all the way to get it to practice volumes (loud drummer), and probably will need to do the same live. A local shop has an old Sunn solid state power amp. I'm wondering if I can make a dummy load for the amp itself, and then use the power amp to boost the power to the cab. Any ideas?
 
#2
You can reamp your head but it might be easier to add speakers or get a more efficient cab. A big part of a tube amp's sound is how the output transformer interacts with the speaker. A dummy load won't react the same way.
 
#3
I don't see why not....if you aren't going to use the 200s at all for driving speakers I would think you could just pull the output tubes and leave it at that, as for driving the power amp, I'd take a signal from the wiper of the treble control and route that to a jack as a line out....here is a schematic of the 200s

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and here is one showing a line out:

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different schematic but same idea.
 
#4
WingKL said:
You can reamp your head but it might be easier to add speakers or get a more efficient cab. A big part of a tube amp's sound is how the output transformer interacts with the speaker. A dummy load won't react the same way.
Click to expand...

I've currently got a 4x12. I'd say it's about as loud and as much projection as the 50w of that amp is going to get. I'd consider adding another cab, but... the 4x12 is a bitch enough to take around live as it is.
 
#5
The problem you are going to face is heat. Dummy loads are in essence resistors. The tube amps power produces heat and the dummy load has to be cooled. The heat has to be expended by bolting the resistor on to a large aluminium heat sink or plate.

To drive the power amp use a 100KΩ 2W resistor in series with a 10KΩ Audio taper pot. Wire this network across the dummy load with the resistor to the hot and the ground leg of the pot to cold (ground). Power amp signal is taken from the pot's slider and ground.

Dummy loads are available from Parts Express. Get the one with the highest wattage 2-300W.
 

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