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tube fanatic

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About tube fanatic

  • Rank
    tube amp designer

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  • Gender
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  • Interests
    extracting the best possible sound from single ended tube amps using modestly priced designs and tubes.
  • My System
    Now specializing in extreme near-field desk top systems using flea power SEPs and SETs. This mode of listening must be experienced as it can be totally enveloping.

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  1. It will be interesting and informative to get your impressions of the amp Joe. Here’s a link to Atkinson’s measurements for those who are as interested in correlating measurements with subjective performance as I am. https://www.stereophile.com/content/yamamoto-08-power-amplifier-measurements Maynard
  2. Joe, you mentioned that you are using a SET in your system. I would bet that part of the problem is the amp’s intermodulation distortion characteristics. Do you have a local tech who can run measurements for you? There are ways to deal with this issue but it may take some work. Maynard
  3. Well, the bias is reasonable. Have you tried phones and looked at the phone jack? Let me know. Maynard
  4. Hey Marty— measure the voltage from pin 3 to ground on the 6BQ5s. The volume pot should not be the issue. Maynard
  5. Jeffrey, as I recall, the power supply of the 345A uses a conventional capacitor input filter with resistors and no chokes. The screen supply is simply split off from an early filter stage. I don’t remember ever seeing one on my bench with a separate screen supply. Is my old memory failing? It should be possible to replace the input level controls with log taper pots and drive the amp directly from a CD player as I don’t recall the input sensitivity being very high. Maynard
  6. Who is going to cut and edge the lens blanks if you buy just the lenses on line, and how do you know what size blanks to order to obtain the correct decentration? Maynard
  7. Are you planning on doing a total restoration? All those caps shown in your under chassis picture must be replaced! I would also look for out of spec resistors as well. Maynard
  8. I don’t mind at all Jeff. However, R7 is just a standard grid leak to bypass any DC voltage created by free electrons hitting the grid and upsetting the bias. There is no negative feedback in use here. Maynard
  9. Jeffrey, if your friend wants a nice, easy, wonderful sounding design tell him to build a pair of Little Sweeties. If you need a link to the schematic let me know. Maynard
  10. Jeffrey, there is really nothing to explain. All I ask is that you show me the square waves at the frequencies that I requested and your calculations of the amp’s output impedance. Maynard
  11. No, I can’t take credit for this one: https://www.americanradiohistory.com/Archive-High-Fidelity/50s/High-Fidelity-1954-Dec.pdf Go to page 107 and enjoy! The designers who read the mail on here will find it interesting. Maynard
  12. This looks very worthwhile: https://apm.activecommunities.com/sfrecpark/Activity_Search/18328 Maynard
  13. Rplace, if you want to learn some basics about power supplies and amps buy this: https://www.ebay.com/itm/Practical-Radio-Servicing-2nd-Ed-Marcus-Levy-CDROM-Radio-Repair-KE3GK/111101526144?hash=item19de2ac080:g:~yoAAOxy--NRwZt0 It explains a great deal in relatively easy to understand language, and has served well as a teaching tool for tube electronics for decades. Unfortunately, the book itself is ridiculously priced. Maynard
  14. Hiss is often a function of amplifier gain. For example, the Krell KSA-250, in spite of its 2.3V input sensitivity, produces a great deal of hiss with Heritage series speakers. Contrast that with the dead silent Quicksilver Horn Mono with a 9V input sensitivity and a power output of 10 times less than the Krell. As far as the power measurement test goes, it is designed to provide guidance as to required power. I find it to be quite accurate. The bottom line is what PWK said is needed to satisfy in-home listening requirements with Khorns. My own experiences mirror this completely. Maynard
  15. All powered devices in the signal path will add some undesirable quality to the signal. Since your amp has its own volume control, I would go with an external switch box to select your various sources. High quality phono preamps are available to go between your turntable and the box. Maynard
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