Up for your consideration: Tone King Ironman power attenuator / load box for guitar amplifierThis is a extremely versatile attenuator capable of an amazing range of tones depending on the amp.  It is a rare, out of production and collectible Mark Bartel design.  Fully functional, Made in U.S.A., Serial No. 1000-70, a couple of scratches here and there.  Front panel: Bypass switch, 0-30db/0-40db switch.  Back panel: amp in, 2x speaker out & line out.  I used it with a Metropoulos '68 plexi amp, a perfect match to tame the amp's output and dead silent (amp for sale on eBay).  Please see detailed photos for item's condition.  Please ask any and all questions prior to bidding, sold as is.  PayPal only, standard shipping due to weight.  Can also pick up in SE Portland and save on s/h - if that's the case, please contact me first.  Thanks for looking!Since its introduction at NAMM 2012, the IRONMAN has emerged as THE attenuation standard. It takes attenuation technology to a new level, with its precision reactive load and 100% pure transformer coupling of both load and speaker at every level of attenuation. With this technology, your amp sees the same complex load impedance at every level of attenuation. The speaker is likewise coupled to the amplifier with 100% pure transformer coupling (no resistors!), for the most transparent and accurate coupling possible, at every level of attenuation. 
This is the sadly discontinued larger Mike Bartel Ironman design capable of handling 100W input with adjustable input and output impedance. The Ironman II does not have adjustable impedance and is only rated for 30 watt amplifiers.  This Ironman has two selectable attenuation ranges along with a true bypass switch, on the rear and a line out. The manual is downloadable at Tone King’s website.