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Vintage Fender Champ 12 Red Knob Repair

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  • Vintage Fender Champ 12 Red Knob Repair

    Hi - My Champ just buzzes like crazy after the main tube heats up - no signal throughput at all. Checked all tubes for continuity; heaters fine (I don't have a valve tester, but the amp was never used much). I can't find A+, but odd readings on B+ (417VDC as opposed to 496VDC) and c+ (297VDC as opposed to 242VDC). All diodes seem ok. I'm guessing one or more of the electrolytics may be duff, but if anyone has advice, I'd be grateful. Phil

  • #2
    Back story? Was it working and it broke? Has it been sitting unused for a long time and didn't work when you plugged it in? If so, did it work before it was stored? flash of light, puff of smoke, dropped from a moving car?

    And please access and post a schematic that we can all reference for ease of communication.
    "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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    • #3
      Hi - thanks for replying. Last time I used it (and was working) was probably 15 years ago. It has been sitting in a decent environment for 10 or so years, but no heating (in the UK). I fired it up a while back and it simply just started buzzing (no *puff* or anything). One of the input jacks was a bit knackered, so I removed IP1 completely just to be sure that there wasn't a short. There has not been any mechanical damage of which I am aware (never been gigged, case OK etc.). I'm using this (http://ampwares.com/schematics/champ_12.pdf) for the schematic.. Thanks for your time!! Phil

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      • #4
        Try with another 6L6.

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        • #5
          Ta. Have just bought a couple.. Fingers crossed.

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          • #6
            Here's the schematic. It does have quite a bit of single ended hum even when working correctly.

            champ_12.pdf

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            • #7
              Originally posted by Dave H View Post
              Here's the schematic. It does have quite a bit of single ended hum even when working correctly.

              [ATTACH=CONFIG]50765[/ATTACH]
              Thanks!

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              • #8
                I would test with another 6L6 as Pedro said.
                But in the meantime you can remove the 6L6, and then measure B+ again. You should see something pretty close to schematic value, probably even more.
                You can also mesure B+ with your meter in AC true rms mode. If you find several volts here that could mean you have bad filter caps in the power supply section.

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                • #9
                  A red knob Fender is vintage now? Good lord, I'm old.
                  It's weird, because it WAS working fine.....

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                  • #10
                    Yeah, sigh...

                    To me 1950s is vintage, but if you are 25 years old, a 30 year old amp is from before you were born. And that is what, 1988?
                    Education is what you're left with after you have forgotten what you have learned.

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                    • #11
                      Yeah, I remember doing warranty work on the red knobs.
                      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                      • #12
                        Originally posted by The Dude View Post
                        Yeah, I remember doing warranty work on the red knobs.
                        Ha , then would that make you vintage?

                        nosaj
                        soldering stuff that's broken, breaking stuff that works, Yeah!

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                        • #13
                          Would it have killed them to include what type tubes are in there?
                          It's weird, because it WAS working fine.....

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