I preamp ed both units with VanAlstine Pat5 SS preamp. The U70 is a keeper, decent power @35w rms per. Clean, sweet highs, tasty mids. Soundstage; better than most! Bass is good for tube, it goes low and full lacking control in damping. Damping factor probably around 9-9.5, my guess...as compared to factor of 10, rated for Fisher X-1000..which I have also compared with, and found to be slightly better at control of bloom. Decay and attack. The Puresonic is a 1965? unit not fully revamped, but freshly serviced w NOS plug in 500v caps installed. Appear to be original Japanese EL34's. Quadramatic includes auto bias feature, among its sophisticated circuitry. Fantastic soundstage! Crisp, but not clinical..even more detail than the U70. I rate the X-1000 more musical than others at mid-highs..it has 55w rms per..new set of output tubes, so more authority present with Martin Logan Clarity's being driven. The electrostats are very revealing, even at low volume listening. I had my friend come over to listen..he said he really liked the sound of the center channel Logos. He was familiar with my set up w three channel Fisher. The only thing was...It was not hooked up to Anything, nor plugged in. It was that soundstage, he heard! He had listened to the U70 plenty of occasions, never a thought it was coming out of center channel speaker! I would say the Puresonic is more balanced over the full spectrum. Its damping factor is 181..best of all amps..back in '64. It had less bloom, better control of bass cones. I set up my Klipsch RF-83's w bi-wired 8ga. stranded welding cable leads attached to woofer lugs. Idea being less resistance to control the woofs. Four twisted 14 ga. 600v solid core wires control the tweets. More skin effect, less conductance between strands, but flexible enough for transport and hook ups. People needed to sleep, but apparent at low level much greater cone motion control over the three 8in cones in each speaker. Really looking for fast tight bass out of a tube amp. I believe I have found my Holy Grail in the 410C. I will update when I am able to crank it! I am also waiting on my Puresonic tube preamp..seems it went into variactic arrest shortly after being arrived. The old boys...including my tech..loved it while it was alive. Cap surgery most likely. Tech loved layout of preamp, but finds amp hard to get at. He hates working on Mac's for same reason. Heralds materials and build quality, though. 42w rms per, less than .05 distortion at any point. IM about non existant. Wonder how it will sound with quality set of tubes? The Fisher was of coarse driven by its internal pre section, Can't wait to hear difference with matched Model 112 pre, for Puresonic. I suggest grabbing one, before someone realizes their inherent value. Not going to say what I paid, but I let the cat out of the bag, now. I'll look for more...but not THE Dizzy Gillespie unit on Ebay! I think he came down to 2500 for 112 and 402C pair. I feel certain same guts as 410c..if you look close at the tag shot..it reads 410C..the front layout is different, than mine. Well let me know if this piques anyone's interest, huh? Ok update, found out tonite..four Valvo 12ax7's(83's) inside, connected in parallel hence the Quadramatic name. so that's what accounts for all that air and soundstage! Found loose connection on one of a pair of GZ34 rectifiers tied together to serve as one full wave rectifier. Tightened the pins, one was Mullard, will have to look for another as match, but the Sovtek in the other works fine in conjunction. Opt trannies are Dyna 70 size, with huge power transformer. I would say the U70 has a warmer midrange, but will See what happens, when tube preamp is in place. Just had fat bottle EL34EH's for outputs, Changed out to 4 fat bottle GE's. Discovered I have 2 Mullard made XF4's...need to find 2 more..hint, I'm looking. I switched out the Martin Logan's Clarity's I was listening to, back to Klipsch RF-83's. The three 8in woofers are ideal for tube amps and the fast bass I want, Sounds even better w GE's. Really wonder what would happen if I put one of the locale's DAC's in play. We have some pretty good locals..AR, Bel Canto, and of course Van Alstine!
