1959 input resistor issue?

Discussion in 'The Workbench' started by NutBuster81, Oct 18, 2021.

  1. NutBuster81

    NutBuster81 Member

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    I built a 1959 clone about 5 years ago, upon completing the project I hated everything about it. Went through 5 sets of JJ el34 tubes in less than a year when the bias was set perfect and burned up an OT. Replaced the OT & switched to EH el34 and it's been stable but sounds like a $10 toy from walmart

    Today, I'm trying to figure out why it sounds like complete garbage.

    I've been checking the resistors on the turret board input resistors and all 4 are measuring 35k in circuit. Is this the problem or do I have to take them out of circuit to test?

    I find it hard to believe all 4 would drop to 35k from 68k but idk.
     
  2. StingRay85

    StingRay85 Well-Known Member

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    Lol you are probably just measuring them in parallel.

    The amp seems to have a totally different issue. Grid resistors have nothing to do with failing tubes or crappy sound
     
  3. NutBuster81

    NutBuster81 Member

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    Idk, it was my first attempt to build this and everything checks out OK except this, maybe it's time to unload it
     

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  4. StingRay85

    StingRay85 Well-Known Member

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    I think you're just measuring them in parallel
     
  5. StingRay85

    StingRay85 Well-Known Member

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    Put a jack inside the channel you're measuring and try again ;)
     
  6. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Learn Ohm's Law and Thevenin's Theorem. Parallel resistors measure as the value of the parallel network, not the component you're trying to measure across.

    If you're burning through five sets of EL34s in a year, you've got a PROBLEM. Don't keep running it, find the problem and fix it.

    Got an oscilloscope? Because you need to SEE how your output tubes are really biased.
     
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  7. NutBuster81

    NutBuster81 Member

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    Thanks, that's what I figured. I'm at a loss as what's going on with it, thought id go back over and double check everything and see if something stood out. Time to send down the road.
     
  8. NutBuster81

    NutBuster81 Member

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    It's not burning up tube's anymore, I either had a faulty OT or unlikely a bad batch of JJ tube stock,

    I don't have an oscilloscope but I do feel like something is oscilla ting as channel 2 sounds big and beefy while channel 1 sounds like a 5w solid state toy amp
     
  9. StingRay85

    StingRay85 Well-Known Member

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    The picture you showed looked like a decent job though. Post more pics and the schematic you used, a Super Lead shouldnt sound like a 5W solid state
     
  10. NutBuster81

    NutBuster81 Member

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    Thanks. I'll post more pictures tomorrow.
     
  11. Gene Ballzz

    Gene Ballzz Well-Known Member

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    @NutBuster81
    I'm gonna bet your main issue is in the power section, bias circuit or possibly even B+ voltage issues! If "channel 2 sounds big and beefy while channel 1 sounds like a 5w solid state toy amp" that can likely be easily tackled, once a good look has been taken at the power amp section! That amp should be glorious!
    Just My Thoughts,
    Gene
     
  12. South Park

    South Park Well-Known Member

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    It sounds like the bad channel has no ground jumper wire the jack ground to center tap . That input is not easy to build you are getting noice so it is trying to work
     
  13. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Went through 5 sets of tubes and an OT? How high is your b+ voltage? Post some pics of your rectifier setup and power tube sockets. There are some really smart people who might be able to spot your problem.
     
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  14. Matthews Guitars

    Matthews Guitars Well-Known Member

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    You can get a decent oscilloscope, even a new one that'll do the job just fine, for 200 dollars or less. Probes may be included, or available for a little more. Just get a 10x probe and a scope that can handle 50 volts/divison, or a 100x probe and then all you need is a scope that can handle 5 volts/division and keep it at AC coupling all the time and you'll have all you need to see if the
    amp is oscillating or if there's a gain loss in any stage.

    As far as I'm concerned, an oscilloscope is the second piece of test equipment you buy after a decent multimeter. And the scope can take the place of the multimeter. Anybody who builds or repairs amps should absolutely definitely have both and know how to use them.
     
  15. Spanngitter

    Spanngitter Active Member

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    For sure not a problem of the JJs or the OT, most likely your Amp is oscillation and punches the sh*t out of the Output Tubes, maybe its missing it's screen resistors...?
     
  16. neikeel

    neikeel Well-Known Member

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    or possibly grid stoppers?
     
  17. NutBuster81

    NutBuster81 Member

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    Pic 1 of 4
     

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  18. NutBuster81

    NutBuster81 Member

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    Ok, it won't let me upload any more pictures....
     
  19. NutBuster81

    NutBuster81 Member

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    Pic 2
     

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  20. NutBuster81

    NutBuster81 Member

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    Pic 3
     

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