Is there anything blatently wrong here?

Discussion in 'The Projects Forum' started by Romes, Oct 15, 2014.

  1. Romes

    Thread Starter Member

    Sep 30, 2014
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    [​IMG]
    This is a 6111 version of the famous ValveCaster. Not to much hype about this version, so not much talk about it on the net. I looked for other builds, with no success.

    Question is, is there anything obviously wrong here? Because I built it, checked it and rechecked it, and nothing.....
     
  2. Lestraveled

    Well-Known Member

    May 19, 2014
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    Wow, 12 volts B+ supply. Shouldn't it be up around 100 volts?? The VI curves say it's not in a linear region at that voltage.
     
  3. Romes

    Thread Starter Member

    Sep 30, 2014
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    All of these ____caster pedals are designed to run starved. So, they do work.... besides that, is there anything I'm not seeing?
     
  4. Romes

    Thread Starter Member

    Sep 30, 2014
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    If anyone is interested here is the original document I started on.
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    I made a living in the 70s playing bass. I understand the soft distortion/compression a tube amp gives you. Looks good.
     
  6. Romes

    Thread Starter Member

    Sep 30, 2014
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    Haha, nice, what kind of music?
    I made a living playing bass for a year here in Milwaukee being in a house band. But no, I did not make that circuit, I was wondering if there was anything blatantly wrong with it......
     
  7. Lestraveled

    Well-Known Member

    May 19, 2014
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    It looks like a lot of the other tube amplifiers I have seen. Maybe the only problem with it is that you haven't built it yet.
     
  8. Romes

    Thread Starter Member

    Sep 30, 2014
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    I have though, and checked and recheck. I emailed the author to see if he has updated since, because mines not coming to life.
     
  9. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    The second tube has no bias
     
  10. Lestraveled

    Well-Known Member

    May 19, 2014
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    OK, I get it now. Of course you have checked and rechecked your wiring and the filament voltage.

    Take an old guitar cord.
    - Cut one end off.
    - Strip off 6 inches of the jacket.
    - Part the braid near the jacket and pull the center wire through.
    - Put some heat shrink over the braid and put an alligator clip on the end of the braid.
    - Cut the center wire to about 1 inch long.
    - Get a tubular .01 uF cap and solder it to the center wire. (Almost any value Cap will work.)
    - Put heat shrink over the cap but leave the lead sticking out like a scope probe.

    This is now your audio oscilloscope. Plug the cord into a working amp, clip the ground lead to the ground of the amp you are working on. Probe around to find where your signal is and is not. Go forth and trouble shoot.
     
  11. Romes

    Thread Starter Member

    Sep 30, 2014
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    Its only one tube.

    And thanks Lestraveled, Ill give it a shot tomorrow! This is the same tool as described on the textbook portion of this site (a transformer with input terminals, .1 caps. and headphone.) right?
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    What he means is you need a resistor in the cathode circuit in order to make the grid bias negative with respect to the cathode.
     
  13. Romes

    Thread Starter Member

    Sep 30, 2014
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    Ahhh, ok ill look over how to calc that and give it a shot, thanks Chips and KL7AJ
     
  14. Romes

    Thread Starter Member

    Sep 30, 2014
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    So, from what I read, pin 5 (2nd Cathode) needs a resister? The other cathode pin has the VR on it....... just would like to confirm before I start adding components to it.
     
  15. Lestraveled

    Well-Known Member

    May 19, 2014
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    If the tubes were being run at their normal operating voltage (125V), you could use the transconductance curves and calculate the correct value, (similar to how an emitter resistor is determined.) I don't think that will work at 12 volts. I say stick a 50K pot in there and adjust until it sounds right.

    Romes, did you do any of the "audio o-scope" troubleshooting we talked about?
     
  16. Romes

    Thread Starter Member

    Sep 30, 2014
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    Not yet, I was going to place a resistor in the 2nd cathode line. Like KL7AJ and Mr Chips were talking about. Trying to figure that out at the moment.

    Wait, so do I need another resistor at the 2nd stage cathode pin? (technically 1st stage, the 50k VR is at the 2nd stage)?
     
    Last edited: Oct 16, 2014
  17. Lestraveled

    Well-Known Member

    May 19, 2014
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    Just a resistor(or pot) from pin 5 to ground.
     
  18. bertus

    Administrator

    Apr 5, 2008
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  19. Romes

    Thread Starter Member

    Sep 30, 2014
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    I didnt not change the R1 yet, I will try though. This is a SubCaster, 6111 relative to the valavecaster. Iv built the valvecaster.
    I will try changing it today and try out the audio oscilloscope as well. Thanks folks.
     
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