AC15c1 Problem

Discussion in 'Amps and Cabs' started by slap_back05, Feb 24, 2015.

  1. slap_back05

    slap_back05 Supporting Member

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    I have an AC15c1 I use when playing bars and stuff so I don't have to drag my UK around everywhere. Last Tuesday, I notice a sort of fuzzy undertone to the sound in the low end, but managed through the gig ok. The next evening it clicked that it was probably tubes, and I had a set of matched 84's so I swapped them and it seemed to fix the issue. Worked fine Friday night.

    Well, Saturday the damn thing kicked on with a weird static-like sound, and nearly all the volume was gone, and what was still there had that fuzzy sound.

    I killed it and replace the pre amp tubes with the last set I still had around, and that didn't change anything. The volume did come up to full and clear a couple times very briefly, but right back to almost nothing.

    Anyone have any tips on what is happening here? I've got a new full set of tubes on the way. Was it the pre amp tubes to begin with, and they cooked two sets of power tubes? Nothing to do with the tubes (i.e. speaker cable?) Or is it something else more major?
     
    Last edited: Feb 24, 2015
  2. Staggerlee

    Staggerlee Member

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    Have you made any mods to it? Like removing bright caps, etc? I had some issues I think due to the low temperatures which developed some cold solders, or rather made existing cold solders worse.
     
  3. slap_back05

    slap_back05 Supporting Member

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    It does have the bright caps removed. Guess I can check/reflow those but just removing the caps shouldn't cause a cold joint problem since there is no longer a component there, should it?
     
  4. Guinness Lad

    Guinness Lad Silver Supporting Member

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    el84s can be a picky bitch. I had a set that sounded great, no issues ever. Decided for kicks to try out different types. Liked the original ones better so I put them back in a few days later. Within an hour they were acting up. These were tubes that had no issues prior, I had to replace them.

    The other issue could be a bad connection on one of the tube pins, it definitely happens, especially if the pins are oxidized.
     
  5. slap_back05

    slap_back05 Supporting Member

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    So give them some deoxit when I replace them then?
     
  6. Guinness Lad

    Guinness Lad Silver Supporting Member

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    Not a bad idea, especially if they were in there and untouched for a long time.
     
  7. slap_back05

    slap_back05 Supporting Member

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    I typically replace every 12 months, but I got either busy or lazy last October and didn't do this one, so they have 16 months on them. I'm just confused as to why replacing power tubes would fix it for a bit, but then it would crap out again. I know tubes can be weird though...
     
  8. Guinness Lad

    Guinness Lad Silver Supporting Member

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    It's because they can get damaged through vibration, this probably does more damage than actual use. Pulling them out and then replacing them could push a pin a bit, or one of the contacts in the amp, it doesn't take much.

    Mine had no noise at all then after I put them back little pops and all kinds of weird things, none of this was red plating, just noise.
     
  9. slap_back05

    slap_back05 Supporting Member

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    Found some different tube and tried again. Then unplugged the reverb tank just to try that. Both times it started with a slightly fuzzy/muddy signal, the cleaned up for a bit, the really faded in volume and got really muddy/fuzzy.
     
  10. Guinness Lad

    Guinness Lad Silver Supporting Member

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    I'm at a loss, if you aren't sure of the tubes you used you need to be doing this with new tubes, nothing suspect. Other than this I'm not sure.
     
  11. TheoDog

    TheoDog Silver Supporting Member

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    Dirty tube pin sockets or a dirty volume pot might be a cause worth investigating.
     
  12. Staggerlee

    Staggerlee Member

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    Again, try reheating the solders on the volume, tone and master pots. Inspect any other suspicious, cloudy looking solder joints and reheat if necessary. Take all precautions to discharge caps before going of course.
     
  13. picnic

    picnic Supporting Member

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    I bought a Bogner Metropolis 15 watter (2xel84)and had it shipped from the Florida store to NJ. It worked fine in the store. Plugged it in at home and played for an hour or so. The reverb channel would go weak and then out. Dry channel worked fine.
    I took it to my NJ tech and he found a small crack in a solder joint on the wet channel. When the amp warmed up, the crack expanded and eventually opened. I've had C1's and they run hot like the Bogner. The tech resoldered the joint and no problem with it from then on. I put a small fan 110v in the cab for extra long gigs
     
    Last edited: Feb 25, 2015
  14. slap_back05

    slap_back05 Supporting Member

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    I'll give them a close look tonight, but I honestly have no idea what I'm doing when it comes to caps and not frying myself, so I will probably just have to take it to a tech if I notice something...
     
  15. slap_back05

    slap_back05 Supporting Member

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    Also, I really appreciate all the tips/advice on this. First amp problem I've ever had.
     
  16. mysticaxe

    mysticaxe Member

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    Check any jacks to ensure they aren't dirty (input, speaker).
     
  17. slap_back05

    slap_back05 Supporting Member

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    Cleaned all pots, jacks, tube sockets, and anything else I could find that had contacts with deoxit. Acted up in the same manner as before, but then after a minute or so went back to normal. Should have new tubes in today.
     
  18. Starquasi

    Starquasi Member

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    My friend had a similar issue with his. Unfortunately, after the tubes were changed something happened (insert science) and the output transformer blew. Be careful!
     
  19. slap_back05

    slap_back05 Supporting Member

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    New tubes last night (with a little more Deoxit for good measure). Was still fuzzy/low volume upon start up, but after about 5 minutes it took off and started to sing. I played for over 2 hours with no problems.

    Will start it back up from cold again tonight and see if it's the same thing.
     
  20. slap_back05

    slap_back05 Supporting Member

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    Conclusion: cold solder joints on the tube sockets. Took it in and had it completely services just in case, but he said that's pretty common and www the first thing he tried, which fixed it right up.
     

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