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Low B+ 5e3

Discussion in 'Shock Brother's DIY Amps' started by Jake Nelson, May 31, 2018.

  1. Jake Nelson

    Jake Nelson Tele-Meister

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    I finished assembly on my home brew 5e3 with a power transformer from a Dukane 1a485c Intercom and it gives me a B+ voltage of 295 volts. So my 6v6’s are running at 65%. My question is, should i change the cathode resistor or would i have better results with a solid state rectifier?
     
  2. printer2

    printer2 Poster Extraordinaire

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    How does it sound? If you like it then great and your tubes will last till the cows come home. It is easy enough to pop out the rectifier tube and tack on a couple of diodes on top of the lugs to see what SS diodes would do for you.
     
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  3. jimgchord

    jimgchord Tele-Afflicted

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    What rectifier tube are you using
     
  4. Jake Nelson

    Jake Nelson Tele-Meister

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    5y3
     
  5. jimgchord

    jimgchord Tele-Afflicted

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    A new production sovtek 5y3 will get you around 35 more volts, so will any 5v4 tube. May or may not make a noticeable difference
     
    Last edited: May 31, 2018
  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    What's the AC high voltage coming off the transformer? I don't see that mentioned yet.
     
  7. D'tar

    D'tar Friend of Leo's

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    Any specs on that PT? Is it hot. i would wonder if it can handle the current draw. If it can, what @printer2 and @jimgchord said!

    Just changing the cathode resistor to increase bias would lower B+ voltage even lower.
     
  8. radiocaster

    radiocaster Poster Extraordinaire

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    A lot of 6V6s, old and new, have a 300V or 315V plate maximum. You can put pretty much anything in there.
     
  9. Jake Nelson

    Jake Nelson Tele-Meister

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    the power transfer was for a 5881 and 8 12ax7’s so it’s good for the current. i’m going to try a solid state rectifier
     
  10. printer2

    printer2 Poster Extraordinaire

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    Heck yeah.
     
  11. robrob

    robrob Poster Extraordinaire Ad Free Member

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  12. Jake Nelson

    Jake Nelson Tele-Meister

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    I did the solid state rectifier mod. Things are looking good now. 351v B+, 324 across the tube, 20v across the cathode resistor at 270 ohms puts me at 11 watts 35 milliamperes per tube
    I also finished up the negative feedback and I like how smooth the amp is with it.
    I do have some hiss that seems to be coming from the Carbon Comp plate resistors on the preamp. I might switch them out someday when I quit playing it for a few minutes...
     
  13. Jake Nelson

    Jake Nelson Tele-Meister

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    By the way, thanks for the help guys.
     
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  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Can you tell a big difference in the tone/feel/output of it with the voltage difference?
     
  15. Jake Nelson

    Jake Nelson Tele-Meister

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    Yes it had breakup before when i was using a 12ax7 in V1 but it was kinda stale. Now, with a 12ay7 in V1, it’s vary responsive and the transition between clean and overdrive is a lot smoother. It’s a lot more sensitive to picking dynamics too.
     
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