I have been planing to build a good dummy load box to my tube amp with a line-out, then re-amp with a quality Solid-State Power Amp into my Guitar Cab. After some research Aikens design seems to load the Tube amp like a speaker would. http://www.aikenamps.com/spkrload.html It includes the resonant peak at the Low frequencies and the slope at the highs. It appears that the big $$$ attenuators are doing just that. Weber, Aracom, Ultimate Attenuator, Power Brake, etc.. Here is my version with a switch between Resistive and Reactive: *All measurements are at 150W (Cranked 100W Tube Amp). LTSpice Redraw: With line-Out and the Line-In Load. Impedance Curves: Switching between Reactive and Resistive. Inductors Currents: Capacitor Current: This equals to AC ripple current in the cap specs. Resistos Wattage: Line Out Pot Steps: Line Out Voltage 0 to 10 on the pot. EDIT 2013: Values have been changed/tweaked for the most accurate results. But the pictures and schematic have NOT been changed !! Final values Page 6 on this thread. http://www.thegearpage.net/board/showpost.php?p=13705647&postcount=84 Final Values. Big resistor 8 ohm (can be 7 ohms for even more accurate results). Treble Resistor 50 ohm for steeper slope (in stead of 22 ohm). Treble Inductor 0.5mH (0.47mH is fine). Resonance Capacitor 200uF (from ERSE Audio). Resonance Inductor 11mH (unwound from original 20mH) 10mH will be perfect here (also from EARSE Audio). Resonance Resistor 75 Ohm, for higher resonance peak (was 33 ohm), you can try even higher to match even better with the real 2x12/4x12 graph. Please read the whole thread if you want to know how it developed and progressed. Keep in mind that the earlier posts are out of date and are not relevant.