Bugera 333XL 2x12 infinium - issue with power tube on slot 1

  1. #1 by Felipe Gonzalez on 02-14-2018
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    Posts: 2

    Bugera 333XL 2x12 infinium - issue with power tube on slot 1

    Hi: I bought a used Bugera 33XL combo 2x12 2 months ago, and I just love the amp sound, it's just amazing.
    However 3 weeks ago I got 2 tubes with the infinium LEDs lit, 2 and 3, so I thought "ok, the amp is used, let's change all the tubes", and I order 4 matched pair EL43 from Electro Harmonix. During this time the amp keep working fine, only the LEDs stayed lit and the standby LED was blinking.
    When got the tubes, cleaned the amp with contact cleaner, as I do with my pro audio stuff, I replaced the 4 tubes, the newer tubes added more "meat" to the sound and all good.
    Last week I was playing and suddenly the amp cut the volume in half, then I checked and the LED for slot 1 was lit, so I turned it off, waited for 1 minute and then turned on and no issues then, meaning the amp stayed working as expected.
    This behavior has been constant since then, but yesterday when turning on the amp I got a very bright tube on slot 1 and then a shortcut blowing Fuse 1, the main one next to the AC connector.
    I changed the tube for one of the old set, since if a fuse is blowing usually it's a failing tube, replaced the fuse and the amp again was showing the slot 1 was failing. I have tried 3 different tubes and all of them are showing the same issue, which is kinda random, no more fuses blowing though.
    Since the amp is out of warranty, because it's used, I am kindly asking where can I look, what can I check, and so on.

    I live in Miami, I wrote to the support department at Care but no reply from them.

    Any help would be greatly appreciated.

    Thanks in advance.

    Last edited by Felipe Gonzalez; 02-14-2018 at 07:45 AM.
  2. #2 by John Butts on 02-14-2018
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    Posts: 27
    Hi Felipe. I'm no techie but since I have the same amp I was curious what the problem could be.
    Here's a couple of threads that may point you in the right direction. Also, as a disclaimer,
    Power Amps can store lethal doses of voltage. But, this can point an experienced technician in the right direction.



    Hello everyone it`s Bugera time again !!! I have a 333xl infinium (killer amp) it has EL34 JJ`s installed with not much hours of use. Well the thing is that in a rehersal the sound just fade away and the standby light started blinking, tubes were not firing up, anyway I took apart the the chasis and found a blown fuse in the F4 position but noticed that the board has a burn mark (refer to photo). After replacing the fuse the amp just started working again but after like 20 min of playing I saw a little bit of smoke coming from the amp, while the amp still on I`ve looked in the board to see were the smoke was coming but I didn`t saw anything. Few minutes after that same thign sound fade away and fuse blown. Since the led lights (tube monitoring) at the back of the amp were on for tubes 2, 3, and 4 I put 4 6L6`s from my other amp and again replaced the fuse, the amp worked fine for 30 minutes no smoke smell but I`ve noticed that the sound was the same but the gain was not the same it has less gain.

    You guys think this could be a tube problem? let me add that after a thorough inspection of the board everything seems to be fine.
    Any advise?


    Photo: https://farm3.staticflickr.com/2859/...69b7d277_z.jpg

    ((Regrettably, the original poster, Fuete didn't indicate a resolution to his problem which appears exactly like yours. John))


    Look at your schematic, the power tube plates are powered even in standby. Check for a shorted flyback diode between power tube plates and ground.

    Bingo .... D4 shorted ... Replaced w/ R2000F ... sparkling tones once more ...



    Last edited by John Butts; 02-14-2018 at 12:05 PM.
  3. #3 by Felipe Gonzalez on 02-14-2018
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    Posts: 2
    Hi John: thanks for your reply. Actually my problem is different than the ones you kindly showed me, however reading in another post here, Michael from Bugera recommended to another user to pull out the 2 outer tubes and reduce the impedance to half to check a failing tube. Since on my case is juts related to the tube in slot 1, I did it, and no more issues so far.
    I don't know if I just have 3 bad tubes but since I don't want to burn another one, and knowing 120 watts is too much for me, I'm fine running with just 2 power tubes and 60 watts.

    Thanks again!
  4. #4 by John Butts on 02-15-2018
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    Posts: 27
    Great idea. It bypasses the pesky power tube 1 slot and you've still got plenty of volume.