Why wont my tubes heat up/glow?? (Amp build fail) HELP

Discussion in 'Amps and Cabs' started by SirGilmour, Feb 8, 2015.

  1. SirGilmour

    SirGilmour Supporting Member

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    Just built my frist amp and............silence. The tubes dont heat up/glow and no sound comes out. As far as I can see all my connections are made and secure. Its a Watts Tube Audio kit for my valve jr. The light in the "power" switch lights up. Ill try and get gut shots up in a bit but maybe someone could help just by looking at the diagram for now.

    Thanks for any help.

    [​IMG]
     
  2. SirGilmour

    SirGilmour Supporting Member

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    To be clear im wondering if any of those connections specifiaclly could cause the lack of tube power. OR would any of them cause it?
     
  3. Jeff Gehring

    Jeff Gehring Silver Supporting Member

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    Check your heater wiring (the pair of wires marked 'twist orange wires together' in the drawing that go from the power transformer to pins 4 and 5 on the EL84, and thence to pins 9 and 4/5 on the 12AX7). There should be approx 6.3 VAC between them. The heaters are what make the tubes glow...
     
  4. SirGilmour

    SirGilmour Supporting Member

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    Thanks. I'll check them now.
     
  5. drbob1

    drbob1 Silver Supporting Member

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    Yup, the heaters are what make the tube glow orange, so that's gotta be where the problem is...
     
  6. SirGilmour

    SirGilmour Supporting Member

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    Haven't checked voltage yet but here are some pics. Go easy on me it was my first build. Haha.

    [​IMG]
    [​IMG]
    [​IMG]
     
  7. SirGilmour

    SirGilmour Supporting Member

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  8. Semitone

    Semitone Member

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    Here is what I would do:

    Unplug the amp, discharge your caps and double check all you solder joints, particularly your tube sockets.

    I can't tell 100% from the photos but some look they might benefit from a further inspection. Better to do it now than after something shorts out.
     
  9. David S

    David S Member

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    There is an inline fuse on the heater wiring near the transformer. Check it or more likely, the connections on the holder. Clean them with a pencil eraser and I bet you are good to go.
     
  10. SirGilmour

    SirGilmour Supporting Member

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    Ok stupid noob question. Which two pins would I put my multimeter prongs on to test the voltage?
     
  11. SirGilmour

    SirGilmour Supporting Member

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    Ok I'm getting zero voltage between them. What would cause that?
     
  12. trailrun100s

    trailrun100s Member

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    how's about putting the negative probe on the chassis, then the positive on the pin...
     
  13. VaughnC

    VaughnC Supporting Member

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    First of all, be very careful as there's lethal voltage in there. You really shouldn't have your fingers in there if you don't know how to take readings. Might be best to have someone locally assist you who knows about electronics?

    If you proceed, you need to set your meter to read AC volts in the proper voltage range and the probes need to be in the proper meter ports.

    You should read approximately 6V AC across the orange wire connections coming from the transformer.

    Also, you need practice in soldering. Any time you attach a wire or componant to a terminal, the connection should be wrapped and crimped with needle nose pliers to make the electrical connection. The solder should only be used to stabilize the connection, not make it.

    Again, be very careful....would hate to lose a fellow forumite over a silly guitar amp. Good luck.
     
  14. SirGilmour

    SirGilmour Supporting Member

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    Thanks so much guys. I'll try a little more troubleshooting but if I don't succeed I'll take it to a tech
     
  15. SirGilmour

    SirGilmour Supporting Member

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    OK so even when the orange wires are unsoldered and free floating in the air I don't get a voltage reading. Also at the top left of the diagram where it says "Tape these three wires off" does that mean strip them and tape them together or keep them isolated and just out of the way of everything? I kept them isolated and away from everything.
     
  16. VaughnC

    VaughnC Supporting Member

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    No voltage on the orange wires means either the PT isn't getting 120vac on the primary or the heater winding is bad. Checking for 120vac on the primary and/or approx. 300vac on the high voltage winding would be the next step...but this is where it gets dangerous for the novice.

    Taping off the wires usually means just insulating the ends with tape so the conductors exposed on the ends don't come in contact with something.
     
  17. SirGilmour

    SirGilmour Supporting Member

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    Sounds like tech time. Thanks again.
     
  18. tuna141

    tuna141 Member

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    Recheck your solder joints. In the last photo, it looks like the leg of the 10Kohm resistor going to the tube socket is not soldered. Also, in the photos it looks like a few components (resistor leads, wires, etc) are running close to other components and some of the screws/nuts. Make sure that there aren't any shorts. Good luck.
     
  19. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Get R17 away from that nut! Physically move it, or insulate the lead


    do you have a fuse in it? Is it blown?
     
  20. Semitone

    Semitone Member

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    This is very exciting.

    I find it more fun to play through my home built 18 watt Marshall clone than any other amps I own...boutique builders be damned. Tone is in the soldering iron of the beholder!!

    Good luck, stay safe and have fun!! :banana
     

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