From Mesa Boogie:

"The Attenuator You've Been Waiting For

Aficionados, this is the power attenuator you’ve been waiting for. One that puts Tone and feel first and includes valuable features you need while preserving the magic of your tube amp in all its harnessed-volume glory.

We start with a reactive Load, an expanded version of that used in our CabClone™ IR series, that protects your amp’s power section and imparts much the same frequency and response curve and reacts with your amp’s power section in much the same way your favorite speaker cabinet does, yet allows you to run silently and safely when a live speaker cabinet can’t be used.

Set to LOAD or SPEAKER, you can take a signal out the optimized LINE OUT ¼” output on the Rear Panel and feed your destination of choice, from Impulse Response players to additional amplification for headroom, consoles for re-amping to effects processors or anywhere an unprocessed signal (no Cabinet Simulation such as that found in our CabClone IR Series) is appropriate.

In SPEAKER Mode, the two ¼ SPEAKER jacks on the Rear Panel function just as those on your amplifier do. In either case, the Attenuator is active and you can use it to reduce the output of your amplifier safely The Attenuation Control in PowerHouse is full featured and provides a Bypass plus 4 Power Reduction levels, -4, -8, -12 and -16dB, with the lowest setting featuring an infinite attenuation LEVEL control that allows whisper soft volumes and below. A Voicing Switch rounds out the Front Panel and includes NORMAL, BRIGHT and WARM settings on the 3-position mini toggle. Output to your Live Cabinets are covered as well with two ¼” OUTPUT jacks wired in parallel, so running additional Extension Cabs is easy. The PowerHouse can handle amplifiers up to 150 Watts and is available in 4, 8 and 16 Ohm impedance versions/ratings."

Brand New condition, with box.