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John Warren

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John Warren last won the day on October 4 2014

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    Engineering-Audio, magnetics, materials for electronic and magnetic applications, engineering models and simulation, SPICE, MATLAB, FORTRAN, acoustics, complex algebra, physics of sound, microphones, vintage audio, loudspeaker design, amplifier design, McIntosh amplifiers, discrete semiconductor devices.....and movies including silents, foreign and indies.
  • My System
    12" Utah Tri-axial drivers mounted in LRE bass "reflex" enclosures.

    Sony Superscope FM only

    Lafayette Solid State Stereophonic Integrated Amp

    16 GA Lamp Wire

    Koss Pro 4AA

    Technics SL-QD33

    CD Player:
    NAD 325i (modified)

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  1. The MC40 chassis from the Korean supplier are really quite nice. I had the factory bottom covers chem-etched and painted.
  2. Truth and good advice, thank you.
  3. Info here: North Reading Engineering
  4. Thank you gents! Yes, it is. I always liked the look of the -1C, the cabinets are old school, 1" thk particle board. Note the equalizer sitting on the tuner. Without either the MQ101 or 102 equalizer the ML systems will have poor bass response so, if you buy a buy a pair without the equalizer, you will be unhappy.
  5. Something a bit different. Retiring from full time work, had time to design a little 7591 p-p amp. Solid state, power supplies for HV and bias suppliers. non-inductive B+, metal film resistors, microphone cable for all small signals. separate circuits for chassis and 0V references, filtered AC input, all metal construction, no sheet metal screws. Top plate is CNC machined, black anodized, 1/4" Aluminum plate stock. Bottom section 300 series mirror stainless, CNC formed directly from my CAD files using SolidWorks. Can use Lundahl or Hammond transformers. Everything but the output transformers sourced from USA. The graphic overlays are the same material plastic lenses for eyeglasses are made from (optical polycarbonate). There's a very cool hifi store a few miles from my place where we gave it a listen for most of the afternoon on a pair of Focals and they'd like to have the amp to show in their listening area. I'll set up but I'm a wee bit hesitant to become an amplifier manufacturer, could be fun but some hassles to. I'd have to set up a facility. Then there's the "how do you compete against the Chinese $800 everything tube amps?"
  6. I'd say that McIntosh used the assembly methods and parts distributors typical of their peer competitors. I agree there's nothing particularly special about their amps other than a somewhat unique output transformer design, i.e. the Unity Coupled Output transformer. Even here however I'd be hard pressed to hear a difference when comparing to other excellent amps of the era. My favorite amp from the late 50s early 60s is later production HK Citation IIs, the units with the Stancor or Magnetics Windings output transformers of which I have two in my own gear.
  7. Next up a pair of MC40s for a complete going over including new chassis parts.
  8. Thanks. They sound like they measure, undistorted.
  9. Here's something you don't see, a %THD v. power plot for a pair of MC30s. The output tubes are new make, matched pairs from JJ (6L6GC), rectifier is also new make JJ 5U4GB. The small signal tubes (preamp 12AX7, phase inverter 12AU7, voltage amp 12BH7 and driver tube 12AX7) are all vintage. The amp pair is shown. Load is 8 Ohm non-inductive power resistor. Plot shows that both amps produce about 30W RMS with <0.4% THD.
  10. Thanks! I too owned MC30s which I sold many, many years ago. I liked them enough but really didn't use them and, at the time, preferred having the cash (June 1988). I've reworked a few pair of MC30s and have done a few chassis replacements on other McIntosh amps, but this was the first MC30 with a chassis replacement. I have a pair of MC40s in the que for the same.
  11. Take the bottom cover off, the factory units are dull, bare metal finish on the underside with ink stamped codes. The new make are mirror like on the underside and no codes.
  12. Thanks Dave. For the amps here, the bottom sections needed refinishing. There's an autobody nearby that will refinish (paint, powder coat) anything made of metal. The paint used here is an acrylic urethane automotive paint (a satin topcoat). After paint is applied, the parts are hung in a benchtop IR oven. Tougher than what a rattle can applied paint provides. The difference between this method and a rattle can approach is the hardness of the paint. Even using a rattle can, an hour or so under the IR improves the durability of the paint. I like the paint shop but I've found another that specializes in small jobs like this and the turnaround is a few days rather than a few weeks. I'll be bringing a set of transformers from a Citation II to them to powder coat in that oddly cool brown color. They match paints using fancy machines and lasers.
  13. In the first post, there's a link to a thread showing photos.
  14. jc- Don't be amazed, the chassis tops are reproductions sourced from Korea. The quality is excellent. The bottom sections were reworked at a local metal refinisher I use. Does enamels, powder coat, anodize, acrylics. And the Korean supplier does make a chrome on stainless chassis top section for the MC225. They have a large collection of top sections reproductions. They've been making them for some time. Fair amount of work goes into the restoration. Most of the hardware is replaced which it should be it's over 60 years old! Good to see the amps in use! Interesting song selection. jw
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