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John Warren

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John Warren last won the day on October 4 2014

John Warren had the most liked content!

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About John Warren

  • Rank
    "So much for the experts on this board"

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  • Interests
    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. Dear God man I haven't even got the prototype built and we're already "upgrading" the design. That said, there really no advantage to going Cu on this particular part but I like your spunk.
  2. The chassis plate for the LK-72A clone and will be shipped from the machine shop in a few weeks. The plate is machined from a 1/4" plate of Aluminum alloy. PC boards and transformer locations are shown in the layout. The PC boards will be mounted to the plate using standoffs. The boards will be enclosed in a cage (red outline in the layout).
  3. When you start worrying about line voltage whatever "fun" there is in this adventure, hobby or whatever you want to call this endeavor is basically lost.
  4. I've been listening to the one described above for about five weeks now and I'm quite pleased with it, even with the low end tubes I'm using. I have a chassis design that is 1/4" thick Aluminum plate that everything bolts on to. I sent the plate out to get clear anodized, and will look awesome! I machined it to accept either the Hammond, Scott or the Transcendar output transfformers. Still lots of bits and pieces to attend to but it's coming along.
  5. Webpage describing break-out and testing. A Wuhan Flu project of sorts. http://www.northreadingeng.com/LK-72A/LK-72A.htm
  6. And here's the Toroidal output transformer version of the amplifier. I had the transformers wound specifically for this project. The output modules are a wee bit different (DC balance and feedback circuits) for both stable operation and enhanced bandwidth. The transformer are also sized for 60W.
  7. Pandemic death grow based on the Gompertz function, it's a s-shaped (Sigmoidal) that's asymmetric about the inflection point. A simple exponential would predict millions of dead in a few months.
  8. Models now show about 84,000 predicted dead from C19. About same as 2017-2018 Flue season. https://covid19.healthdata.org/projections?fbclid=IwAR1TzhAOpQza4HELTO8C6RtytagXnX3LcWXbSg9EtWjCSNxynzTsM3MdTPk
  9. Fauci has stated that C19 could cause between 100-200k deaths in the USA when it's run its course. Fauci wouldn't have made estimates if he wasn't comfortable with the magnitudes. Note that the Seasonal Flu in 2017-2018 caused an estimated 61k deaths. So the C19 is 2~3X greater burden on the healthcare system than the 2017-2018 Pandemic Flu. https://www.cdc.gov/flu/about/burden/2017-2018.htm?fbclid=IwAR2DXA33LUOkiC4ad9W5_zGuzHTfysAZ8SM6U2ByGeXtGjuMDhrBVOXirO0
  10. Leave it alone. Measure the Anode current of V4 and then on V5, compare. The amp should be at idle, no signal at the inputs. A close approximation of the current can be obtained by using a DVMM (FLUKE 117 for example) switched to mA DC with the common lead (BLK) clipped to the 380VDC B+ center-tap on the output transformer primary and the positive lead on PIN 7 of V4 (and then V5). The readings should be close say 2mA within each other and measured at the same B+ voltage. If they're off, say by 4mA or more then one tube is working harder than the other and push-pull symmetry lost. When the two are working in symmetry the 120Hz HV ripple in the B+ line is cancelled out (common mode rejection). Note that Anode current varies with wall voltage because B+ varies with wall voltage. There is risk of electrocution when making these measurements. The measurement raises the DVMM to the B+ potential, in your case about 380VAC. A good DVMM can perform this measurement with no issue. Do not use probes, the safe way (the only way I would do it) is using Pomona mini-grabbers or probes with extendable clips. On the meter side banna plugs that hold fast. If you short the B+ to ground you'll explode the 380V supply. Make the two connections with the amp off, set the meter to mA DC and preferable bring the amp up to 117VAC with a Variac whilst monitoring current draw and B+ voltage. The amp (or Variac) should have the proper rated fuse or one 1/2 amp lower. Then repeat for V8, V9.
  11. The center-tap at the 380VAC secondary section is a floating chassis ground. The RCA phono plugs jacked into the amp from any source with a three-prong plug will tie the "floating" chassis ground of the amp to the Earth ground prong at the wall socket. If hum goes down in volume, the signal has a low impedance path to ground and sinks to the wall prong.
  12. I haven't given that question any thought. Not clear yet if I want to offer the boards for builders, it's a bit complex. I also want to get the pre-amp sections build and tested but the Coronavirus shut my PC board supplier down on the west coast. Power output should be in the 30W RMS/ch. The 1650Ps are 60W transformers.
  13. CHA and B distortion with the Hammond 1650P output transformers at 1kHz (GRN, RED) and 15kHz (YEL, PURPLE). 15kHz testing is very hard on the tubes. Load is 16Ohm resistor on each channel. For a tube amp, the responses are quite good!
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