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  • #1

    hum problem?

    Hey guys, i have just finished a matchless lightning clone build and I'm having some hum issues.the amp sounds fine untill I increase the master volume and the higher i turn it up the more hum I get. The power tranny doesn't have a center tap for the hearter winding so I used 2 100r resistors. I've checked and re-checked all wire conections and can't seem to find any problems there. all grounds seem to be good and I've switched out all the tubes and still no success. any ideas where else I can check?

    chuck.
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  • #2
    A layout pic or link is needed. If that is not available, a complete description of all ground and chassis connections.
    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !

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    • #3
      +1
      Hum may be the most variable thing to troubleshoot. Asking why an amp hums without ALL the info on layout and grounding is an impossible scenario. I've seen posters faced with this that have posted a generic schematic of an amp with the explanation "It's almost just like this amp" or something like that. That doesn't help. We'll need a schematic of your exact amp as you believe it is wired and photos of all the work along with diligent follow up to responses and willingness to follow suggested tests and checks.

      I'm not being a hard ass. This is the only way it works. Otherwise you end up with a ten page thread, a few angsty responses and an amp that has NEW problems because of all the invasive surgery. We've seen it happen a few times.

      A good, generic test to isolate the problem and minimize the amount of info needed is the tube pull test. Start by pulling the first preamp tube. If the hum doesn't stop pull the next one....
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        I hear you loud and clear chuck. I should've posted pics of the amps wiring layout. I didn't have a camera on hand at the time of the question and I was frustrated trying everything I had learned from you guys in the past in relation to my hum problem.I stepped back from the amp for a couple of days and went back at it refreshed. I found the problem almost right away. It was the main ground for the board, which was not getting a good connection to the chassis. I removed the connection from the chassis and roughed up the chassis surface and re-installed it,problem solved. Thanks for all your help in the past and I certianly appreciate it. Next time i have a problem I'll be sure to post schematics,pics,etc to help in identifing the problem.

        Chuck.

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        • #5
          Good that you found the problem.If I might say,those types of connections suck.I would suggest after cleaning the chassis,solder a bit of solder to the chassis around the hole for the screw,replace the screw and the ground connection and then heat the connection ring till it becomes soldered directly to the chassis,you can then put the nut back on if you want,but not necessary.Those nut and bolt connections often become oxidized,a soldered connection wont.

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