They basically work like a second master volume. They do NOT let you get power tube saturation at lower volumes. Only a proper attenuator (Webber MASS, HotPlate etc) can do that.
anyone else
it says you CAN get that cranked tube sound, but i dont see how that could ever work through the effects loop
An attenuator goes between a head and a cab, and controls the volume from the head going into the cab. This way you can crank the head and still be able to turn the output down to a normal level so you can get the sound without the volume.
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