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Jeffrey D. Medwin

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About Jeffrey D. Medwin

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    Forum Veteran
  • Birthday 11/27/1944

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  • Gender
  • Location
    50 miles East of Kansas City, MO.
  • Interests
    Audio, music, and the stock market, ..............is there anything else ?
  • My System
    Two stage Direct Coupled DIY triode amps, careful wiring, very lightly-modded professional - use speakers.
  • See My System

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  1. Right, you do not overheat the tip or the joint. Apply 120 VAC for just a matter of seconds. I am totally aware of that. Use of 0.62 diameter solder, fed in, helps cool the tip a bit too. There are advantages when using such a 325 Watt unit, that no one has yet acknowledged or thought about . My audio mentor, Dennis Fraker, tells me he has used a WELLER D-550 for about 50 years now, for perhaps 90% of his amplifier work. Dennis finds its use to be indespensable. Jeff
  2. That photo posted on 07-08 is somewhat blurry, mediocre, and I don't see how anyone can tell whats really going on there. In real life, with an LED work light of many lumens, the joints look OK to me, and I think you folks would likely agree. I appreciate everyone's concern. It just doesn't strike me as being an issue, in real viewing. Thanks. Always appreciate constructive input. Please keep it up !!! I do wipe the tip off with that Weller D550 regularly. Jeff
  3. I understand your comments, and appreciate them. The Mil Spec wire ( m22759/11) is of very high quality construction. Multi stranded copper, each strand silver plated, teflon wrapped. As a private party, one can source this wire at SURPLUS prices, easily. Try eBay, or perhaps best, Apex Jr. in Southern California, Torrance, CA., at reasonable prices, on a cost VS performance basis. I never set-out to build this preamp the way everyone else does. It has got what "I" want it to have internally, such as each B+ node is double series SHUNTED, and each B+ node will also be double Final Filtered ( L1/C1/L2/C2 ). Imagine a phono preamp that draws 180 mA., 70 mA. for the audio circuit, and 110 mA. for its SHUNTING circuitry. Jeff
  4. Cookson Electronics ALPHA Reliacore 15 solder, 63-37 0.062 diameter. Weller D-550, 325 Watt setting.
  5. 7-8-2020 PROGRESS PHOTO RCA Jacks to Tube Socket : Doubled up Cardas 19 AWG "Polished Silver "wire from M. Percy. Ground Busses ( 3 : left, right, and IEC ground ) 10 AWG m22759/11 10 , copper multi stranded, silver plated, .........stripped of Teflon jacket. Direct couple, between two 12AX7s stages, Siltech LS38 - IQ, ...........superb wire.
  6. Jeff Rense often reports on UFOs, peruse his wild site . Jeff Medwin
  7. A typical tube rectifier has two plates, is called a " dual " rectifier.
  8. Most rectifier tubes, eg: 5U4GB, has two plates inside, it is a dual rectifier. Less resistance : TWO raises the B+ voltage versus one, perhaps by about 8 VDC. PSUD2 it and see !!
  9. The early McIntosh MC-60 push-pull monoblocks had dual rectifiers, and always preformed quite nicely, as did the Industrial McIntosh MI-200 "shaker table " amplifiers have multiple tube rectifiers. When you go to dual rectifiers, you halve the impedance of the rectification function, which is a lot like halving the DCR ( direct current resistance ) of the rectification function. Executed properly three ways : (1) with equal length wiring, (2) a separate power transformer for the rectifiers' filaments, that is (3) connected in absolute phase with the main B+ power transformer, and one can get sonic gains. Only if done properly. I have experimented with one, two and four rectifiers...... in the 1980s. Read this letter to me from a friend, Charles A. Halijak. He was Dean of the College of E.E., at the University of Alabama and he wrote to me about multiple rectifiers. GREAT guy !! Please see " Clue Number TWO, 1989 " : https://community.klipsch.com/index.php?/topic/182623-kt88-direct-coupled-design/&do=findComment&comment=2381499 Have fun !! Jeff
  10. The goal in a two stage DC SE amp, is to get both tubes to operate well, and also to operate together as one, well. Certain things are done on an artistic, and " determined by listening basis. ". It may, or may not, be to your liking, and that is OK. I will post my 6FQ7 graph, and you will see it is done mainly as a exercise, to see how well the tube will operate, with AVAILABLE PLATE RESISTORS, because without a really GOOD sounding plate resistor, I have little interest in building any amp. Mech Engr Vic could chime in, on what a plate resisitor swap alone, did on his ST-70. In the above graph, you can see, I considered in this order , the following Value Plate Resistors / resistor anode / Ras : 38.3K, ( red ) 37.5K, ( green ) 36.5 K, ( blue ) and as of yesterday , not denoted above,......................... 34,050 Ohms. ( 2 times 68.1 K ) The Golden Ratio, is reoccurring in nature Maynard. Another key factor, not mentioned in (1) through (9) in an above post, is that one can't go too wild with current draw, when using LSES ( low stored energy supply ) filtering, because ripple will be excessive. So, there are ten trade offs to simultaneously consider, all at once Maynard. After 13 years of doing these DC SE amps, I have a decent handle on what seems OK to do, and what to avoid. Yes, I hear the thermal stress sonic signature, and purposely avoid it. Plus, I like designing-in long term tube life and having long term reliability. I will give the nod to a more vibrant sound, over a graph, any day of the week. Notice, the 6FQ7 above is operated at 180 VDC , plate to cathode, in ALL cases. That type of priority, is what separates an E.E.'s build, from an artist, or, any person who designs primarily by ear. The 5K is the Rk for the KT88, when it is direct coupled. The KT88 operates into a 2.5K Ohm SE Output transformer, Magnequest DS-025. I do not always worry about lowest distortion, but rather, dynamic capabilities, etc, and the LSES supply and wiring, can support a 2.5K output !! I am not worried one iota about my friend in India's auditory capability. If something sounds really really good, it is good. Most tube audio amps I hear don't cut it. So users have a choice, and different people will all choose differently ............what might someone prefer, cancer, polio, or just a small staff infection?? Jeff Medwin
  11. It is a simulated ( PSUD2 ) balance, using real world value standard value resistors, not actual measured.
  12. Don, About the only time I will measure wire is when I am assembling speaker leads, amp to crossover, or crossover to drivers. Oh, and I DO make all my AC cords two Futon increments. 114 1/4 inches. That is it. When you design with triode tubes, they are essentially linear in nature, in their transfer function. IF ( a big word ) you know how to employ them, operating-point wise, the measurements YOU are thinking about are typically not needed. Of course, all else in the build has to be accounted for, with much forethought and care. Yesterday I used PSUD2 , doing VDC simulations, to help an audio friend living in India, designing his first DIY SE DC monoblocks. I enjoy doing that. There is not a doubt in my mind that his DIY mono amps will play well, and the only measurements needed can be done with his DMM, to be sure the circuit resistances, VACs and VDCs, simulated in PSUD 2, are correct. I spent 5 1/2 hours straight yesterday, doing his PSUD2 simulations, until I was happy with obtaining target voltages that closely balanced the direct couple. With a 502 VDC B+ supply, I was able to obtain a BALANCED DIRECT COUPLE ( where each tube was being optimally operated ) using STANDARD resistor values, to within 0.03 VDC. That close voltage balance is not too shabby , when you start out with 502 VDC. I operate tubes in their linear regions, and VERY conservatively. His 1/2 of a 6FQ7 Driver tube is operating at 16.4% of the plate's maximum rated dissipation. His KT88 Output tube operates at only 29.1% of its rated maximum dissipation. That conservative KT88 operating point relieves the burden of large amounts of unbalanced DC, upon the Single Ended Output transformer. That sounds better !!! Of course, all else in the amp has to be ( and is ) uniquely designed ( ultra-low DCR magnetics, really good wiring to maintain transfer efficiency, dual 5U4GB rectifier tubes, and a thoughtful lay-out ) so as to be able to obtain a successful overall result. I am choosing all his build parts, as part of my specification, parts proven to sound good !! His finished monoblocks, two stage, direct coupled, zero negative feedback, will likely outplay most of the audio amps out there, I am thinking. It does not need to be " measured " except with a DMM. Audio design of tube amps is not solely science, it is also an art. Results count, not particularly what you can see on any piece of test gear, but rather, ultimately, it is what you hear - and how you feel, when playing back music that is meaningful to you. Does it continuously thrill you? If so, .......you are there !! Jeff Medwin
  13. Hi !! What if you were to input an audio signal to the grid of V3 or ......maybe even better, V4. If the extreme gain of V3 is not needed ( a 12AX7 has a mu of 100), one less stage for the music signal to go though should certainly sound better. Perhaps try both, I see no huge risks,............... but I have only looked at this quickly and casually without much thought. Tubes don't blow up like solid state devices. Try inputting into V4 first, then perhaps V3 and V4. Tell us how it goes !! That stock rectifier tube is a whimp, power supply peak current delivery - wise. A 5U4GB would be better, but it has a 3 Ampere fuilament requirement, and the stock rectifier tube winding may be insufficient. Jeff
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