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John Warren

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John Warren last won the day on October 4 2014

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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
    Speakers:
    12" Utah Tri-axial drivers mounted in LRE bass "reflex" enclosures.

    Tuner:
    Sony Superscope FM only

    Amplifier:
    Lafayette Solid State Stereophonic Integrated Amp

    Cables:
    16 GA Lamp Wire

    Headphones:
    Koss Pro 4AA

    Turntable:
    Technics SL-QD33

    CD Player:
    NAD 325i (modified)

Contact Methods

  • Website URL
    http://www.northreadingeng.com

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  1. Did a complete overhaul on this 333A. New Al- and Ta-electrolytics, many new transistors. The goal was to achieve like new performance. I have many of the HP special BJTs including the Germaniums from this era. The 333A and 334A were popular distortion analyzers from 1968 to about 1980. They're actually very useful for measuring THD+N in tube amps but good luck trying to find one in good working order. They're straightforward to rework but getting the best out of them isn't so simple. The key to getting these units to operating "like new" is the voltmeter circuit, it must measure accurately to the micro-Volts level and that's not so straightforward. How does the analyzer work? A signal is applied to an amplifier to be tested for distortion, say a 1000Hz sine wave signal (the fundamental). The amplified signal is then sent to the analyzer where the operator "tunes" a Wien bridge to "notch out" the fundamental leaving the harmonics and noise for measurement by the meter circuit. The accuracy of the analyzer is governed by the accuracy of the voltmeter and the accuracy of the meter circuit over the bandwidth of the instrument (5Hz to 600kHz). Below is the signal source, a 100uV, 400Hz sinewave signal which requires specialized instruments to source. And the measurement of the 100uV sinewave at the 333A is below. The meter range knob (lower right) is set at .0003 which is 300uV or about 1/3 of a millivolt at full scale. The magnitude of the voltage is read at the 0-3 graduated scale. Note the pointer is at 1 or 100uV. The 333A and 334A units are useful to about 0.03% THD+N which is about 30X higher than current state of the art units, like the Krohn-Hite shown above which is capable of 0.001% THD+N.
  2. The build "quality" on the Crimson-ring thing was absolutely, decided garbage. Why would anyone give these clowns a penny?
  3. That has virtually no impact to the layout.
  4. Here's a project I did a year ago. The measurements are the most basic, 1kHz THD and bandwidth. Without even listening to it, I'd state it will sound pretty good. But, do the measurements tell the whole story? No. Swapping the 5AR4 rectifier for a solid-state plug in improves the low end a bit which I don't need a plot to tell me, I can hear it. I can however measure the difference in 20Hz distortion and the temperature of two resistors. The hotter resistors mean output tube life will be lowered. A compromise I'm not willing to take. Why? Because the amp, as is, satisfies everything I look to a tube amp to satisfy.
  5. The tube crisis is manufactured. JJ can easily supply the current demand. For those that are in need, you're being played. JJ is shipping but $ are still x3 what they were this time last year. Wait.
  6. The PC board layout was done by newbie.
  7. Then there's the price point. How much would one be willing to spend on a match pair of, say 7591s? 80USD? My guess is the new WE will come in closer to 300USD. So 600USD for your Scott 299C. I was ready to pull the trigger on a new amp build based on the Citation II. That will not happen. Anyone interested in buying a tube amp should think long and hard about that purchase, you might be stuck waiting for 2 or 3 years before your EL34s or KT88s are readily available.
  8. In 2019 a J&J 7591 was $16. In June they'll be $125 each. Good luck with that bros!
  9. I had one and managed to score a second. They express voltage on a log scale allowing 5 decades to be captured on the swing of the needle pointer. Useful to measure voltage across a load resistor for amplifiers under test. The right unit is the first issue, 1968, all gold traces. The left unit is the last year of manufacture, 1976, Pb-Sn traces. That unit also needs a knob, which I found on-line and ordered! Measures both VAC and VDC from 1mV to 100V and dB equivalents.
  10. Losing djk was a big hit to the local audio community in general. I miss his contributions here and elsewhere.
  11. It's a statement amplifier: Carver has decided the vast majority of buyers are too stupid to know better.
  12. Boards came in a bit earlier than expected. Checking first that the pc board hardware can be installed. Bass and treble pots. I'll start a separate thread on the preamp. Board mounted RCA terminals as inputs.
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