AP1 & AP1X Power Amplifiers

One Response to AP1 & AP1X Power Amplifiers

1. tupebakil3 says:

   August 26, 2015 at 12:44 pm

   Look at the McIntosh MA230 carefully. It shows the right way to do the cahdtoe-and-plate-windings thing, which you also see in some Fishers, the original Quad, and lessee, that Bogen there. I found this ad awhile ago-it’s for a now finished eBay auction-and whoever the seller is, I think he knows his stuff. I put it on Usenet:<<These are one pair of Output Transformers for the McIntosh MA230amplifier. These were bought NEW by me directly from McIntosh inBinghamton in or around 2009 for a project I had planned but neverstarted. They were the last pair that McIntosh had in stock, from arun by the original vendor (either Endicott Coil, Endicott NY next toBinghamton or Magnetic Windings, Easton PA, who made the Marantz 8Band 9 transformers for VAC when they did the reissues) done sometimein the late 1980s.One is in the original sealed box as shipped by McIntosh Binghamton.The other has been opened for inspection and will be repacked andresealed. A pivotal role in the resurgence of DIY tube amp building was playedby the MA230 output transformer when Bruce Rozenblit of TranscendentSound found a supply of these and designed a project using these,which he wrote up in Glass Audio magazine, "Build 70 Watts of McIntoshPower". The project became such a success the original supply oftransformers was exhausted and McIntosh authorized the original vendorto supply a third party-I think it was Audio Classics in Vestal-withanother run of these (at least 100 pieces) and Mc themselves bought afew for replacement stock as interest in the 230 had greatlyincreased, plus calls from DIYers. I bought the last two for aproject, which I have decided not to pursue. Bruce's amp ran a pair of 6550 or KT88 tubes at a pretty high B+ (inthe fashion of VTL which was the in vogue high end amp at the time)for about 70 watts midband, with 20 Hz response somewhat down fromthere. Later, Richard (RiMo) Modafferi designed an EL34 amp he wroteup in Glass Audiio as well which was much more conservativelydesigned, using as I recall EL34 tubes. The original MA230 was rated at 30 wpc but these transformers wereseverely overdesigned for that. Between 40 and 50 watts is probablythe best realistic rating for them.These are NOT the McIntosh "Unity Coupled" multifilar primarytransformers used in the MC-30 through MC75 amplifiers, which werewound in house on C-cores. They are conventional transformers exceptthey have a cahdtoe winding similar to the Quad II. Because of thefeedback these provide, the driver circuitry has to provide a fairamount of drive to the control grids of the output tubes. These areNOT an upgrade for Dynacos! You can copy the MA230 circuit, useBruce's or Richard Modafferi's circuit from Glass Audio, or designyour own.Many listeners who like HIGH FIDELITY and not the signal modificationof SETs and such have claimed the MA230 when operated as a straightpower amp is the best sounding amplifier Binghamton ever put out. Ihave heard Bruce's project amp and a version of the RiMo design (withsome minor changes) and both were amongst the finest tube amps I haveever heard. The tubes run conservatively-the original MA230 used the7591, a tube I dislike personally, but even so tube life is generallysuperb as compared to other conventional amps. (The Mc class B UnityCoupled amp will get the longest life of any tube amp from tubes butthe sonics are a matter of taste with some listeners.) These may be the best output transformers in the world you can buynew in box. Here's why: They were made by the original vendor (Brianthe parts guy didn't know but ex-Mc employees have told me it had tobe MW or Endicott) at a time when they still had (many or most of)the original female wind operators as when these were high volumeparts, the original fixturing, but modern wire insulation andadhesives. I am a former transformer/coil plant test technician and will explainsomething no one talks about. In any transformer plant all the winders(on electronics size parts, i.e., not power pole transformers andbigger) are women. WINDING TRANSFORMERS IS WOMEN"S WORK and I do notmean this as a pejorative: they deal with the fine motor skills neededfor fine wire handling and the repetitive nature of production windingmuch better than the men do. The men get bored and goof off and eitherquit or get fired. As with vacuum tube manufacture, the highest quality transformers aremade in large quantity by staff who do a lot of them and whose work isunder constant QA analysis. Calibrated test equipment and a rigorousprogram involving testing and occasional teardowns of assemblies andfeedback to the operator as to where she went wrong is feasible onlyin such an environment. Don't be fooled by boutique vendors thatconsist of one or two guys with a bunch of wind sheets they pulled outof dumpstars and a worn out Universal winding machine who are windingthem in the rumpus room full of cat hair and potato chips when theyget an order or two. They CAN NOT consistently achive a uniformproduct, and they don't. Insist on transformers made by professionalsin a business environment with cross-checking by multiple people whodo it all day. << The poster points out that Magnetic Windings of Easton, PA wound the original Marantz 8B output transformers. That isn't quite right. The original Marantz 8 used outside sourced transformers, from a now defunct company, and several companies bid on the job including Peerless. The 8B used in house wound transformers and Sid Smith had the prints, not Marantz, and Sid Smith being Sid Smith wasn't giving them up for love nor money. Sid and Dick Sequerra both think they are the only people who can do what they do, etc. MW may have bid on the job and had A design that was competitive, but they were NEVER the vendor to Marantz when it was in New York on the 8 or 8B. When Marantz Japan wanted to reissue the 8B, along with the 7C and the 9, they went to a third party, VAC in Florida, who in turn went to MW with a couple of original parts and what prints they had. Between testing, teardowns, and a few iterations of wind schemes, MW came up with the REISSUE 8B transformer which is better than the original. Will they do any more? Maybe if you asked they would, I don't know. The previous commenter talks about the VTL designs. VTL when David Manley ran it, made amps that were pretty much derivatives of British Partridge designs, using the same five-and-four, all leads out secondary scheme most British high end transformers did. Mercury Magnetics (yeah, the company with the hokey ads in Vintage Guitar magazine) did a slightly bowdlerized Radford clone OPT, the VTO-100, for most of these. It was a good transformer and a good amplifier save for the huge filter caps and no soft start circuitry of any kind: many of the power transformers have endured one too many THUNKKKKKK!!!s and started buzzing or opened a winding in the twenty years since the David Manley, simple, not grossly overpriced VTL era. Neither Luke nor EveAnna knows foc's'l from futtock plate about electronics, sad to say, and the Stupid Money has made the prices go nuts.

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