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John Warren

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John Warren last won the day on October 4 2014

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About John Warren

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    "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. EV published the DIY plans for the Georgian and sold drivers for the enclosure. The woofer should be a 15W K, the K is stamped into the rear badge for Klipsch. The DC resistance is 3.1-3.3Ohms. The issue with these old drivers is the voice coils are fragile and can't take much heat. They're tube era drivers. The Georgian was EV's version of the Klipschorn which they licensed from Klipsch to produce.
  2. And you can install a 1A fast or slow blow fuse in the Variac to limit current draw regardless of what the Amp meter shows. Regarding the amp meter, I use a Fluke that measures in mA AC. Most tube amps idle at about 1000-2000mA. I have a dedicated VAC meter on the setup as well.
  3. I purchased a Citation II. The important bits and pieces are there and it sounds good but it needs a good going thru. The chassis is in good shape and the transformers are fine. Every other piece, including the boards will be replaced. I'll restore the entire thing to museum quality and when I die leave it to one of my kids.
  4. I have no hobbies, I'm just an engineer.
  5. Ignoring the cost, which is considerable for high end audio components, driver entitlement becomes a near reality when the enclosure is rigid. Although the images are from the Magico website, Aluminum enclosures machined from plate stock are nothing new. I heard a pair of JBL L100 clones fabricated from 7/8" Al-plate, milled and assembled using cap screws and Loctite adhesive. It was heavy but easily managed once placed on a dolly. Internal bracing resulted in the overall enclosure being somewhat larger than the OEM version. The difference in the low end performance is hilarious.
  6. Entitlement in the audio reproduction "chain" isn't in the electronics or even the loudspeaker drivers, it's in the enclosure materials. And the folks fabricating enclosures out of Aluminum alloy are on to something. It's a "ffs" moment listening to them.
  7. 99.999999% of audio amplifiers are voltage sources. If transconductance amplifiers were a better mouse trap, the world would have marched to them immediately. Why do you think it did not?
  8. Short of cracking open a 7591 and just looking at G2, the datasheets from all the old suppliers state that Pin 8 and Pin 4, which both make internal connections to G2, are to be externally connected via jumper for "efficient" operation of the screen. The cold resistance between P8 and P4 is 0.2-0.3 Ohm, i.e. a short. So that's got me curious, why the external jumper? I can speculate it's due to the way the grid is made, two sections connected by grid wire that, when operating, develops a hot resistance large enough to sustain a potential difference between p8 and p4, a difference enough to alter the screen grid performance. Anyone actually know?
  9. Took some time but the Lundahl units have arrived. They're 25W RMS, 6K primary 4/8/16 Ohm secondary, C-core transformers. Here's the primary side of the output transformer, eight solder pins. And here's the secondary side, sixteen tinned wires. The enclosures are optional, total cost with enclosures is $625 for a pair. The secondary is a bit of a pain to wire. To measure the primary impedance, I temporarily soldered it for an 8 ohm load per the schematic below. GREEN is the primary impedance of the Lundahl with non-inductive, 8 Ohm load and, for comparison, the Hammond 1650PA PURPLE and the Scott OEM output transformer, GOLD. The Lundahl is a bit flatter than the other two. Output tubes are 7591s in push-pull arrangement.
  10. I have no doubt that vacuum tubes today can be made vastly better than what the OEMs could provide. Vacuum systems, glass technology, materials supply chain are all better. And there still is, today, a large presence in the high power, vacuum tube industry (radar and communications). There are plenty of highly skilled technologist in the vacuum tube industry. Look up, Travelling wave tubes, cross-field amplifiers, Klystrons, Magnetrons. But, is there a business case for such an investment in audio grade vacuum tubes? I would propose no, there is none, too costly and the returns are not there.
  11. New Mom's use it in baby formula too.
  12. is the only water you should use to saturate your solder tool sponges with. Don't use tap water to wipe your soldering tool tips clean, the Chlorine, Fluorine and salts will corrode the plating on the tip and shorten tip life by half. It's literally free at our supermarket (0.99/gallon) with 3 year shelf life. To be called distilled, the total solids content can't exceed 10ppm which is pretty spectacular given your paying about a buck for a gallon. Don't use Di-ionized water either, it will attack the tip.
  13. Spent Friday last listening to the Transcendar and Hammond output transformer versions of the amplifier. I have a well broken in set of Sylvania 7591s that I was using, swapping them from one to the other. Speakers are JBL L200s. I also revised the feedback on the Hammond to provide a bit smoother response above 50kHz. Here's the distortion curves for both channels with the Transcendar outputs and Sylvania tubes, virtually identical. There's a leveling off as the power approaches 8W RMS or so then there's a significant rise past 15W RMS. The plates can dissipate 19W RMS. Same tubes with the Hammond outputs. The Hammond is rated for 60W, a much larger core than the Transcendar which is a 22W transformer. And here's the amps How did the sound? Hard to discern a significant difference between the two but I did like the Hammond version better. The L200 isn't that good in the mid range and the bass is "tubby" but, that said, both amps sounded good to my 62 y/o ears. I was plugging a 24-bit CD player directly into the RCAs, no preamp. The distortion curves were taken after my listening so I wasn't entirely biased based on measurements.
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