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Need CL help

Discussion in 'Amps [BG]' started by Floyd Eye, Jul 4, 2013.


  1. Floyd Eye

    Floyd Eye Banned

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    I went to rehearsal this morning for the first time since the outdoor gig we did last weekend, in which we got rained on. I got all the amps covered pretty quickly though and as far as I know none of them got wet.

    Anyway, guitarist gets hooked up first, turns on his JSX and nothing. No light, nothing. So I pull the fuse and it's blown. Replace it, works fine. So then I get hooked up and turn on my SVT CL. After 5 minutes or so I turn it off stand by and I hear a loud pop followed by a loud hum. I immediately turn off the power. I check the back and make sure everything is hooked up right and turn it on again. Loud pop followed by loud hum and a blown fuse. So I replace the fuse and turn the amp on with it in standby. The stand by light is flashing green and red now. Turn it on and blow another fuse. So I take the grill off the back, check that the tubes are seated and replace the fuse. Then while I am looking at the tubes I turn it on and off standby quickly and I can see one power tube lighting up bright white while simultaneously the loud hum is going on. So I switch that tube with the tube next to it and do it again. The same tube lights up bright white and hums loudly.

    So my question is this. Is this just a blown tube or does it sound like something else is wrong? If so, obviously I have to replace at least those 3 ( am I correct in assuming that the 3 to the right are together and the 3 to the left are together?) but is that really ok or do I need 6 matched tubes? If I replace the tubes with matched sets, do I need to have anything done internally to the amp or is it all good as long as I have the external bias knobs set correctly?


    Any help would be greatly appreciated as I have a gig next weekend. Thanks.
     
  2. B-string

    B-string Gold Supporting Member

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    You had a tube fail. You can sub in one tube to be sure the amp operates. Then replace that triplet only if you wish.
     
  3. Floyd Eye

    Floyd Eye Banned

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    I have no spare tubes. So if I am going to buy tubes I need to buy them in sets of matched 3 correct? I wish I had an extra to make sure nothing else was wrong. Dammit.
     
  4. B-string

    B-string Gold Supporting Member

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    Yes a matched triplet. Save the two (most likely still good) tubes for the next time (if there ever is). Chances are good nothing else is damaged but stop dropping fuses in it with that tube before you force an additional failure.
     
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  6. Floyd Eye

    Floyd Eye Banned

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    Will I need to take this to a tech and have it biased or can I just put the 3 new tubes in and use the bias controls on the back?
     
  7. B-string

    B-string Gold Supporting Member

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    You can follow the bias instructions to get it fully operational. If you hear or see anything odd then see a tech.
     
  8. Floyd Eye

    Floyd Eye Banned

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  9. B-string

    B-string Gold Supporting Member

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    Last note if you buy the same brand tubes as you have now you will have the most predictable result. Different brands can have a slightly different sonic character.
     
  10. Floyd Eye

    Floyd Eye Banned

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    The amp has all Sovtek 6550WE's in there right now. So what if I replaced those 3 with Winged C?

    Also, I just got to thinking, if I had removed that tube and the one from the same slot on the other side, that would tell me if there was something else wrong wouldn't it?
     
  11. B-string

    B-string Gold Supporting Member

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    Removing one from the opposite side will tell if the amp can operate, but it needs to be fully loaded to be SURE everything is okay. Winged "C" have a different sonic character than the WE's. If it would sound different better/worse I can't say.
     
  12. Floyd Eye

    Floyd Eye Banned

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  13. Mark Reccord

    Mark Reccord

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    This sounds like a bad tube for sure.

    However, the power tubes are matched pairs not triplets. I don't remember the layout of the CL but I think there's a diagram on the inside of the amp. If you could even get a matched triplet (seems unlikely as most amps operate with push-pull pairs) you'd end up with mismatches.

    What you need to do is figure out which tubes are the push-pull pairs and pull the pair with the bad tube. Once you do that you can power the amp back up to make sure it works. If it powers up ok with that pair out, you can either replace all of the 6550s or just the pair with the bad one.

    I'd be inclined to replace all of them with a matched sextet of the reissue Tung Sol 6550s, but I realize that's a pretty expensive route to take.
     
  14. Floyd Eye

    Floyd Eye Banned

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    On the CL I am pretty sure the 3 on the left are opposite the 3 on the right ( push/pull). I never heard of a CL that ran in pairs. Are you sure you're thinking of the right amp?
     
  15. B-string

    B-string Gold Supporting Member

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    Yes Mark that is incorrect, the CL uses six output tubes. Each triplet has independant bias adjustment.
     
  16. Mark Reccord

    Mark Reccord

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    Yep. Absolutely sure. All push-pull amps use pairs of tubes and the push-pull pair is where matching is most important.

    I think the CL power tubes are paired front to back (can't remember for sure) so if you replaced the 3 on one side and not the other you'd have 3 mismatched pairs and an unbalanced (and possibly unbalance-able) power amplifier section.
     
  17. B-string

    B-string Gold Supporting Member

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    Sorry no, check a schematic online. Push and pull sections are defined by the "side" of the output transformer they are wired to.
     
  18. coreyfyfe

    coreyfyfe Supporting Member

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    The SVT uses two trios with independent bias adjustments. One the CL/VR they're arranged in triangle shapes like bowling pins. As long as the three of the triad are matched you should be able to bias that side fine.
     
  19. Mark Reccord

    Mark Reccord

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    It does have 6 output tubes: 3 push-pull pairs.

    And yes both the push and pull sides of the amp have independent bias controls but if you look how the amp is actually biased, it requires that the push side be biased identically to the pull side, i.e. 0V between the test points on either bank of 3 tubes. Matching between the pairs is more important than matching the 3 push tubes and the 3 pull ones, because if one pair is biased slightly differently from another pair (assuming the pairs are matched), that doesn't affect the balance of the power amp. However, an unmatched push-pull pair does affect the balance and may make it impossible to bias the amp properly.
     
  20. Mark Reccord

    Mark Reccord

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    Yeah, there are 3 "push" tubes and 3 "pull" ones, just like in any push-pull amp with 6 output tubes. You can indeed bias the amp properly with 3 different matched pairs but good luck doing it with 3 matched tubes on one side and 3 matched but different ones on the other.

    There's a reason the vendors sell matched pairs and not matched triplets. :)
     
  21. DiabolusInMusic

    DiabolusInMusic Functionless Art is Merely Tolerated Vandalism Gold Supporting Member

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    I am quite positive they are matched triplets as well, but obviously you folks know more about this than I do. I treated them as triplets, as did my tech, as did every other person I have heard mention the SVT power tube section.
     

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