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Need help; 5F1 build completely dead.

Discussion in 'Shock Brother's DIY Amps' started by teek_s, Sep 21, 2020.

  1. awasson

    awasson Poster Extraordinaire Gold Supporter

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    Heater wiring looks correct on the preamp tube. I can’t make it out on the power tube. It looks right on the regulator as well but I’d double check just to be safe.

    Because your indicator light is dead and nothing glows, I still think the heaters aren’t getting voltage. think the safest way to test is pull the tubes and check if you’re getting heater voltage at the indicator or whether there’s a short somewhere there. You can check most of the heater voltages by probing the tube sockets.
     
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  2. teek_s

    teek_s TDPRI Member

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    Thank you! Hopefully I'll get to the hardware store tonight and get what's needed to make a lightbulb limiter.

    Sorry about that! I'll try to clean up some of the wiring.
     
  3. tubegeek

    tubegeek Friend of Leo's

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    Maybe a little tape over this junction (white AC lead/black transformer lead) until we get things further finished please? IMG_20200921_115329.jpg
     
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  4. teek_s

    teek_s TDPRI Member

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    Haha, got it! I had it soldered and taped, then I think I stressed the metal a bit too much and it broke off.
     
  5. tubegeek

    tubegeek Friend of Leo's

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    Wait - so that was the problem spot?
     
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  6. teek_s

    teek_s TDPRI Member

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    Sadly, no. The neutral is connected, just not soldered.
     
  7. tubegeek

    tubegeek Friend of Leo's

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    :(

    Ok onward and upward then.
     
  8. Linkjr

    Linkjr Tele-Meister

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    Is there a connection between the tops of the first 2 large blue filter capacitors on the left.
     
  9. teek_s

    teek_s TDPRI Member

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    There is no connection between the two, and from what I think you're getting at I'm going to assume there should be.
     
  10. awasson

    awasson Poster Extraordinaire Gold Supporter

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    Let's get back to the heaters and indicator lamp. No light, no heaters, no amplifier.

    With the tubes out, do you see somewhere around 6.3v A/C at the indicator socket when you turn the switch on (it will be greater than 6.3v without tubes to load it down)?
     
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  11. Linkjr

    Linkjr Tele-Meister

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    I'm not sure which schematic / layout you used to build the amp better to follow that. Or post it up. But if you look at post #4 there is a layout and you can see there should be a connection in this layout.

    Be careful these capacitors hold a big charge make sure they are drained before proceeding.
     
    Last edited: Sep 21, 2020
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  12. jmp81sc

    jmp81sc Tele-Meister

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    I am also seeing damage to the black primary wire that is connected to the on/off switch. Make sure that is not broken. At least put a wire nut on the white wire from power chord to the transformer primary black wire. Latter solder and heat shrink the connection or use a terminal to anchor them to.

    I can't see any grounding on the board except the first two filter caps. Is it under the board?

    As others have already said, no tubes and get your AC correct. 120 volts going in to the output transformer. Around 5 volt going to the first tube socket yellow wires, 6.3 plus going to the other two tubes at the green wires. Without tubes these voltages will be a bit higher.

    as a side note your lead dress will need attention. this amp will probably be noisy once you get it up and running, but first things first get it working then address that.

    Good luck and welcome.
    John
     
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  13. teek_s

    teek_s TDPRI Member

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    Just tested this, and there is no voltage at the indicator socket, or the wires for that matter.

    I think you might be right about the damage, I tested and there is no continuity between the two primary leads.
     
  14. teek_s

    teek_s TDPRI Member

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    MY GOD YOU WERE RIGHT ABOUT THE DAMAGE!

    I'm so sorry, it turns out the flimsy primary wire of the power transformer decided to break, although the PVC coating was still in the hole so I didn't notice there was no connection. Again, I'm so sorry to take everyone's time. Thank you all so much! I'll have more updates on the way!
     
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  15. teek_s

    teek_s TDPRI Member

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    So, the indicator light turned on and everything was working fine with rectifier. I then inserted the 12AX7 and the fuse was blown. I'm going to check all the grounding and all the connections, then try again with a load attached.
     
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  16. Diverted

    Diverted Tele-Meister

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    Excellent. Given that there was no power anywhere, I figured it could very well be an open winding on the power transformer primary, or a miswire in the switch/fuse/transformer etc. Checking for continuity from point to point is the most direct way of finding if connections are properly being made.
     
  17. Diverted

    Diverted Tele-Meister

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    Check for short circuits/stray wire strands bridging pins etc. Also check all the things that should be grounded by measuring for continuity from the point that should be grounded, to the chassis.
     
  18. awasson

    awasson Poster Extraordinaire Gold Supporter

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    This is excellent news!

    Now you know where the first problem was, corrected it and you can go through and fix the rest. You'll need to trace the circuit and make sure there are no shorts.

    Before you do, you’ll want to make sure the amp is unplugged and that the electrolytic capacitors aren’t holding any high voltage. If a capacitor is charged and has no way to discharge, it will hold the charge indefinitely. Test the capacitors with your meter every time before you start working on an amp and you’ll be much safer in the long run.

    By the way, welcome to the site. You’re at the right place.
     
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  19. tubegeek

    tubegeek Friend of Leo's

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    .
     
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  20. BigDaddy23

    BigDaddy23 Tele-Holic

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    Build a light bulb current limiter, mate. It will help you troubleshoot safely and will go a long way towards protecting the trannies and you, for that matter.
     
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