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Bugera 333XL problems with Crunch and Lead Channel

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  • Bugera 333XL problems with Crunch and Lead Channel

    So, I've had a Bugera 333XL for a few years and I've never had a problem. Last night I turned it on and now I have a problem. The clean channel is perfectly fine, but the Crunch and Lead Channels have almost no sound. I can hear it if I crank all the way on the master and channel volumes, but ultimately the signal has suffered a massive loss. Is this a tube issue or something else? Please advise.

  • #2
    Bugera used a weird numbering layout.
    The first tube that the signal sees is labeled V8.
    So working from the input jack end Clean & Dirty use V8.
    At that point Clean goes to the FX loop.
    Dirty uses V7 & 1/2 of V6.
    So if you have a spare 12AX7 you could try swapping out V7 & 6 one at a time.
    Short of that, this amp utilizes relays to switch all of the separate channel features.
    Tech time if that is the case.
    Last edited by Jazz P Bass; 10-27-2013, 09:24 PM.

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    • #3
      Solution

      Check R123 (with the amp turned OFF) on the pcb B+ plate voltage resistor to V7/b. should read 1 or dead or nul. i tried a couple times to upload schematics. but this site keeps timing out. just fixed same amp same problem. check resistence on R94=100k, R95=150k, R123=150k, R93=100k. you can throw a 100k in there in place of the 150k wont hurt or notice the difference. also recommend 1/2 watt instead of 1/4. piggyback new resistor ontop of old dead one and solder it to the dead one then clip out the dead one. this way you wont have to pull the entire pcb. should take less than 10 minutes. you can email me for the schematics

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      • #4
        Since the big server crash, files don't like to upload if they are already here. I think the 333 is already posted here. If it has been corrupted, we need to reload it but resize it first.
        Education is what you're left with after you have forgotten what you have learned.

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        • #5
          I recently repaired a Bugera 333XL with this exact symptom. What I found was an open plate resistor to B+ on one of the 12AX7 preamp tubes. Simple fix, cheap and quick. Sorry, I never did find a downloadable schematic for the amp and was simply troubleshooting the old fashioned way so I don't recall and specifics about which tube it was.


          Steve
          Pacific Music Services

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