What could have went wrong with replacing a tube socket?????

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by hottub, Feb 20, 2009.

  1. hottub

    hottub Member

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    well I replaced a bad tube socket today and all the leads are soldered back where they should be. (I took a pic prior to removing the bad socket so I'd be sure to have the leads back on the right pins). All solder joints seem good and the tube is nice and snug, but when I fired her up, I get nothing at all. All the preamp and power tubes are lit up, and the fuses seem fine. I had sound prior to doing this repair.

    One thing I'm questioning is...could I have drained the filter caps wrong, causing something to short out?

    I have a multimeter. Any ideas what I can check first?
     
  2. VanR

    VanR Senior Member

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    Bad tube maybe?
     
  3. Blue Strat

    Blue Strat Member

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    Is the filament lighting up? If not, check the voltages to those pins and check the soldering. What kind of amp is this?
     
  4. JerryP

    JerryP Member

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    +1 what kind of amp? Post the before and after pics.
    Jerry
     
  5. hottub

    hottub Member

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    It's a '85 JCM800. Tubes seem ok. Tried 3 other ones that I know are good. Solder joints seem to be ok.

    [​IMG]
    [​IMG]
     
  6. RussB

    RussB low rent hobbyist Silver Supporting Member

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    Maybe some soldering flux and/or solder ran down into the socket and is making poor contact with the tube's pin(s)
     
  7. Rosewood

    Rosewood Member

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    No matter how good your eyes are it's a good idea to use a magnifier to look at the solder joints.
     
  8. hottub

    hottub Member

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    I also took some readings of the cans and can only get a reading from one of them. One is like 500v and the other one doens't read anything at all. And also nothing reads on the plate voltage too even though the power tubes are lit up.
     
  9. AR-305

    AR-305 Member

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    Are you sure you didn't blow a secondary fuse when you "discharged" the caps?
     
  10. hottub

    hottub Member

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    a secondary fuse? do you mean the two on the back panel? I put two good ones in the holders and fired her up and still nothing.
     
  11. VaughnC

    VaughnC Supporting Member

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    If replacing the socket was the only thing done, in that scenario, I'd start by using an ohm meter to verify continuity between the socket side and the terminal side of all of the pins of the new tube socket. I suppose it's possible that one of the socket pins could be internally open or the contacts could be sprung too far apart.

    Also, some modern tubes don't have pins thick enough to make good contact with tube sockets designed around NOS type tubes. Did you try an NOS type tube in the socket?
     
  12. hottub

    hottub Member

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    guys, thanks for all the suggestions and taking the time to reply and help out. I feel like a total fool. I spent countless hours this weekend trying to figure this thing out and ultimately went back to the fuse area. It turns out that, although both fuses were good, it was the fuse holder that ended up being the culprit. for whatever reason the spring inside the holder was either backwards or fully depressed in such a way that it wasn't applying pressure on the fuse itself in order to make a connection. I popped the spring out of the holder and put it back in the way it should be and viola! we now have a rip roarin 800 again!
    I'm also wondering if this could have been a contributing factor to my initial problem of the amp cutting in and out while playing it under high volume conditions. for all I know the fuse could have been loose inside the holder the whole time.
     
  13. AR-305

    AR-305 Member

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    The absence of B+ voltage was the giveaway. Sounds like you've found your gremlin.
     
  14. The Pup

    The Pup Supporting Member

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    All's well that ends well.
     

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