Speaker Load Substitution

[hal9000]

Anybody know where to get Mesa tranny voltage info to plug into P = V^2/R.

If you use a 4ohm load instead of 8 or 16 ohm, will your amp always sound louder in dB's? Higher wattage according to formula above. Change in tone?

What are the Rectos, Stilettos, Mark IV's, etc. rated at in watts @ x ohms?

Mesa's amps are rated for the same power into both 4 and 8 Ohm loads because the output transformer has multiple taps designed to make the load look the same to the tubes.

The power equation doesn't apply to tube or SS amps in the way you're thinking. SS amps do increase the output power per lower impedance (until they melt down), but it's not necessarily linear, so can't count on the formula.

 

[hal9000]

thanks for the reply hal. I've read a couple tube amp books as well as some Mesa owner's manuals and didn't learn that. Good to know.

So basically, if you run your Mesa amp into 8ohm or 4ohm speaker load, the wattage remains the same and in terms of decibels, there will be no difference.

I wonder if that's true with other amp brands as well.

You're welcome and yes, for other tube amps with matching OT taps, the power will remain the same as long as the speaker impedance is matched to the OT's tap.

Power tubes have a pretty high nominal output impedance on the order of 3-5 kOhms, so no matter what, you'd need an output transformer to get down to speaker level impedance. SS output sections are very low impedance, for example a few ohms or less, so they can drive speaker directly with the need for an OT.