Only selling to help fund another audio project. I bought these and have put maybe 50 hours on them. I will include buyers choice of a quad of Electro Harmonix KT 88 or a quad of Tung Sol 6550 re-issue. Price is FAIR and FIRMThough not pictured I do have an original pair of cages that are still brown and the Dynaco badges were removed otherwise they are near mint The balance of the tubes included are RCA Cleartop 12au7 and GE Vintage 5au4 Rectifiers. Below is the description by Chris Keller The tech that Did the restoration on the amps Buyer covers shipping and Fees if any "Here is a beautiful pair of Dyna MK-III mono amplifiers up for your consideration. The MK-III's were the second generation power amps after the MK-II's from Dynaco. With their massive A-431 output tranny's, each amplifier puts out 60 watts using KT-88/6550 output tubes. They'll drive any speakers with ease. Like the later ST-70 stereo amplifier, it is really critical that they be updated with more modern power supply filtering and a new driver circuit to be operated safely, and of course more sonically accurate. As such, these were restored from the ground up. The power transformers, while working, were tired and humming pretty good. Not surprising for 60 year old power transformers operating beyond their 115 volt rating for the past 40+ years since we've gone to 120 volts and higher household voltage. I decided to purchase new, properly rated drop in replacements from Dynakit parts, to avoid any future issues. They run quiet and cool.
Another critical update for these amplifiers is having properly rated power supply filtering. The original power supply filter cans usually have dialectric like oatmeal at this point. They must be replaced. The initial power up surge voltage on these amplifiers runs high, so I used Miec electrolytic caps rated for 600 volts to handle it. The power supply is now nice and stable. and the caps run cool. The original 6AN8 driver design was certainly adequate, but produced (for lack of a better term) more of a one dimensional sound. The original boards of course were way beyond the expiration date with contaminated traces. The VTA driver circuit uses two 12AU7 tubes, which are readily available and inexpensive and provide dozens of opportunities for tube rolling if desired. The VTA boards also house an updated bias circuit and provide the opportunity to bias each output tube individually, so you do not have to have a perfectly matched pair of output tubes. I've added bias test jacks in the rear of the chassis to make biasing these a snap. Other upgrades on these MK-III's include new cooler running ceramic sockets replacing the older brittle micanol types; all new wiring throughout; modern binding posts replacing the original terminal strips, and the impedance can be changed from 4 to 8 ohms with a switch in the rear; new RCA jacks and new heavy duty power cords were added, along with a new power switches. These MK-III's do still have the original hand wound cloth lead A-431 output tranny's, which are the heart and soul of these amplifiers. Cosmetically these amplifiers look terrific. The tranny bells and laminates were removed, sanded and repainted satin black, and the original chassis were sanded primed and sprayed in an oil rubbed dark bronze metallic finish. I also added cool VTA plexi covers over the driver boards and nice walnut front fascias. In all, they look really sharp. Wife approval will be no problem with these. Tubes are RCA cleartop 12AU7 drivers, new pairs of Tung Sol 6550/KT-88 output tubes and G.E. 5U4GB rectifiers. Ok, so how do they sound? In a word, superb! They run dead quiet and produce a hearty, tight bass, an ultra sweet midrange, and the beautiful wide classic dyna soundstage. Over $500 of upgrades were done to these amplifiers, not counting the time I put into them, though I do love bringing these old jewels back to life. They should be good for another 40 year run!"
| 
