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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. Hi Eric, Thanks for posting the Vacuum Tube Valley 2A3 amplifier shoot out results, which I was previously not aware of. There are two very simple, pure common-sense reasons why Craig Uthus' Moth amp would come out on top in that comparison back then. Assuming all the amps tested were well-designed : Reason 1) A well-designed two stage SE amp will always out perform any well designed three stage SE amp. Why ?? simply because there is less parts and stages that the signal has to travel through, with less chance of the signal degrading. Reason 2) Direct coupling is the highest fidelity way of coupling two stages. It is impossible to out-perform a length of highest quality solid silver wire, used to transfer the audio information, from one stage to the next !! The second best way, fidelity-wise, to couple two stages is a Interstage Transformer. But its GOT to be a good one. The third, and least-best way, to couple two audio stages is with a film capacitor. So, all of the above, becomes the common-sense reasons why I DIY design and build and listen, strictly to two stage DC amps for personal use, for the last thirteen years. Use the very best topology. Once this is understood, why would anyone waste their time, money, and life ..........using approaches that are second best in topology / design ?? Many many implementation-advancements have been made since the old Moth execution was available. Seems like, every week we find new subtle ways to improve audio amplifier performance. Lots of DIY discovery occurs. Jeffrey
  2. Congratulations !! The tech, conservatively, kept essentially the same parts types ( Solen supply caps ) so there is no issues of re-voicing the amps, which is good. Enjoy your music, now that all is fresh and working as originally intended. No need to leave amp "ON" all the time, if that is what you were doing previously. !! Its hard on tubes, etc. Jeffrey Medwin
  3. There seems to be much discussion on speaker efficiency in this thread. I suppose because of use of a JJ 2A3-40 amp. Question : Does the system gain an additional 3 dB , when a second speaker ( for stereo ) is added?? Is there any measurement continuity .....of a Manufacturer quoting efficiency to the public testing in mono, or quoting to the public testing with a a pair of stereo speakers?? I often have wondered, about the above. Ideas, comments?? Thanks! Jeffrey
  4. Go on line, to Frank's Electron Tube Data pages, and download the data sheets on a 12AT7 and a 5U4GB, and read what they do !! Also, download data sheets on the 6L6GC, and do your own homework. No need to bother your builder when the data is readily available. You VERY MUCH have to bother builder - for a nicely written set of instructions for each and every switch he put on that chassis !!! Switches improperly positioned - create failure modes. Personally, I am not a fan of tube amps designed for public use, with any user-adjustments on them, other than an on and off switch . Thank goodness, you are now on top of this from the get - go. Consider taping the switch instructions, a neatly typed synopsis on ( or inside ) the amp's bottom plate, ( if its not used for ventilation), as a back-up in the future, for your grand kids to see. I also would ask him now for a schematic and operating voltages, so this amp can be easily repaired / maintained in future decades, without having to reverse engineer his design, by a repair technician. You are a customer, he will likely be happy to give you that information. Jeffrey
  5. Hi, it can NOT ever be a rectifier tube, as part of the middle audio-amplification stage !! A 6N3C is like a 6L6 power tube, Russian. Look it up on line. The EH 5U4GB absolutely IS the amp's rectifier tube., it is positioned on the amp chassis in the front, middle.
  6. By all means .......have your builder clearly write down what the switches do, and give it to you . Give the amp at least 75 hours use to allow it to settle in. Stopping and starting it, normal use, is swell !! Have fun.
  7. The smallest 12AT7 is the input tube. A 5U4GB is a rectifier tube, part of the power supply. He used a Electro Harmonix, my personal favorite 5U4GB tube choice in 2019. The EH 5U4GB takes 75 to 200 hours to fully break in BTW. The middle sized tube between the Input tube and the Finals/2A3 tube is a " Driver" tube, which drives the Finals tube. This is a three stage amp, Input ( 12AT7), next a Driver ( not specified yet ) and Finals ( JJ 2A3-40). The JJ 2A3 is among the best cost VS performance choice today in 2A3s when properly operated.
  8. The JJ 2A3-40 tube has a 2.5 VAC rated filament. So does a Type 45 have a 2.5 VAC rated filament. A 300B has a 5 VAC rated filament. Current draws may vary between these different size and type tubes, ( eg : the 2A3 and the 45 ) and that will effect the actual operating voltage at the tube socket . Jeffrey
  9. The rectifier tube should located be as FAR away as possible, from the input tubes. Here, we see just the opposite, close-to and smack dab between both of the input tubes.
  10. You need to do your homework, before throwing money at a vacuum tube amp. You truly do not have the knowledge ( yet ) to discern what the best high end amp is , IMHO. Also, since you have little experience, please consider NOT buying new, as the losses when you upgrade will be maximized, when buying new. I recommend you look at used amps. Consider Decware, Quicksilver, as a starter, all USA made, companies with a good track record, quality, performance and reliability wise. Be sure that what you spend, you can re-sell it for , because people change amps, looking for higher performance. You will select differently as you discover " your " ultimate amp to own.. Hence, my " buy USED " suggestion. Take your time, do your homework, LEARN, have fun. Jeffrey
  11. Thats highly unusual. I have never heard of a 2A3 with a 5 VAC Ef rating. WHAT brand is it ?? ( AMP and Tube ) You know, for 100 years plus.... its been 2.5 VAC. Every data sheet I have read. The 2.5 VAC Ef is one of the advantages of the 2A3 tube, because AC heating at 2.5 VAC sounds better than DC heating. Educate me please !! Thanks. Jeffrey.
  12. Takes a while to load. Hope you enjoy this half as much as I did ! https://www.nytimes.com/interactive/2019/06/21/opinion/editorials/errol-morris-lobster-sviatoslav-richter.html Jeffrey Medwin
  13. KISS rules !! Each and every part you add to a system, degrades the signal, and overall possible performance. That extra line stage you have added is certainly an overall sonic degrade, simply because of all the extra parts the signal has to travel through. You would be much much better off simply improving the parts in your original basic attenuator, by doing some research and using a) the BEST possible all-silver contact switch systems and b) best possible resistors, c) Best solder, and d) best silver wire ( how about Mundorf Silver and Gold wire) , ... doubled up for maximum transfer efficiency ???? e) and the shortest / simplest signal paths. What should be discussed is, what ARE the best possible parts available to us in 2019 ? Never bundle signal wires, separate them. . Your work is very neat, BRAVO........ but its far to complex and unnecessary in my opinion. Jeffrey
  14. Copper plays the mids. Silver content adds high frequency response, as is wider band and more conductive. Pure silver is cost prohibitive. In 2019, April on, I use a stranded copper, with each strand individually silver plated. 133 strands of 29 AWG , in a teflon jacket. Military wire. 8 AWG !!! $2.00 a foot on eBay, or Steve at APEX Jr. M22759/11 8 or 16878/4 or 16878 /5 ( 600 and 1,000 VDC rated) in 8 AWG.
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