'66 Fender Vibrolux Reverb Issue

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mmp31, Feb 1, 2015.

  1. mmp31

    mmp31 Member

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    When the amp is cranked, I am not getting nearly as much volume as I should. It's probably 10+ dB quieter than usual. It started happening the other night while I was playing. While the amp is quieter, it's also distorting a lot more. Anytime I strum, the power tubes emit a bright ultraviolet/blue color, which disappears when I stop playing. I've never seen this before because the power tubes are usually glowing orange.

    It's doing this when I'm plugged into both the Normal and Vibrato channels, so I don't think it's a bad preamp tube. I thought perhaps it was a bad power tube, but I stuck a new pair of power tubes in tonight, and nothing changed.

    After a couple of minutes, I started smelling something burning, so I shut the amp down and tried to locate where the smell was coming from. I'm almost certain it was coming from the power tubes. Neither of the transformers were hot but the power tubes seemed hotter than I would expect them to be after two minutes outputting low volume.

    The rectifier tube is still glowing bright orange, so it appears normal but I can't say for sure that it's functioning properly.

    Before this started happening, the amp was making intermittent popping sounds and also intermittently would drop volume for a couple seconds then return back to normal.

    Any suggestions?
     
  2. zenas

    zenas Member

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    Do a google image search for red plating tubes. If your plates are glowing orange you have a problem a big problem.

    Do you know a tech? Because it sounds like you need one. What's the history of the amp? Has it ever been serviced with new electrolytics?

    Sorry if I sound like a dick but from your post it sounds like you have no idea what your doing.
    Hopefully I'm wrong.

    The long and short of it is you have a 2,000 dollar amp that's going to be an 800 dollar amp if this keeps up.
     
  3. mmp31

    mmp31 Member

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    Why would I do that?

    If the plates were glowing orange, I would have said so. I didn't, now did I?

    I might, but I'm not paying somebody if it's something I can fix myself.

    It has the original power transformer, choke, and reverb transformer. Before I bought it a year ago, the previous owner replaced the output transformer with a Marvel Electric P-TF22848 and also replaced the electrolytic capacitors as well as several resistors and signal caps. Also the amp is using Sovtek 5881 power tubes instead of 6L6GC's.

    You don't sound like a dick, you are a dick. You inaccurately concluded that the tubes were red plating, and you refused to make any other suggestions other than tell me to take it to a tech, which isn't any help. The real question is do YOU have any idea what you're doing?

    If what keeps up? The amp keeps sitting around unplugged?
     
  4. zenas

    zenas Member

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    If you would have posted a little history in your OP and said the plates aren't glowing orange then maybe I wouln't have assumed your just another dumbass about to burn down an amp.

    Then I could have started from a more informed position and I wouldn't look like a dick.
     
  5. mmp31

    mmp31 Member

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    Why would I explicitly state in my OP that the tubes are not red plating if they're not red-plating? By that logic, I could have sat here all night listing issues that the amp doesn't have. I don't see how that would have helped.

    Do you have any suggestions or are you just here to troll?
     
  6. zenas

    zenas Member

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    Nope just trolling I don't know nothing about them old Fenders. Good luck with it.
     
  7. Greentone

    Greentone Member

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    So the new guy (mmp31) seems like fun...
     
  8. BobK

    BobK Member

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  9. pdf64

    pdf64 Member

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    See https://www.kcanostubes.com/content/blue-glow-tubes
    Are you sure that the emission is bright, rather than faint, eg would it be reasonable to described it as 'bright' under normal office lighting levels?
    Or is it only really noticeable in low light conditions?

    What static dissipation are you setting the power tubes to?

    Have you tried the amp with a different speaker cab (of similar impedance / type)?

    Are you competent to use, and have access to, an electrical multi meter?

    Are you competent to de-energise an amp / take the chassis out of the cab, and check eg resistors?

    Are you competent to check voltages in a live exposed amp chassis?
     
  10. Kurzman

    Kurzman Supporting Member

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    Op:
    I think the guys here usually want to help but advising on working on an amp is kind of a tricky thing because you can actually kill yourself messing around with these things if you don't know what you're doing.
    And the techs on this board have no way of knowing if you're able to work on a "hot"amp safely.
     
  11. Blue Strat

    Blue Strat Member

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    Because you're asking advice of people who know what they're doing and need background info to help you.

    People come here all the time furnishing minimal information and leaving out very important clues.

    The next things we need to know are:
    a) What's your idle plate/cathode current of your power tubes?
    b) Do all the voltages in your amp check out compared to the schematic?

    If you can't furnish both of these pieces of information you need help from qualified tech.
     
  12. gldtp99

    gldtp99 Member

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    If this amp was in my shop with these symptoms I would:

    1) Pull output tubes and test them

    2) Pull preamp/PI tubes and test them

    At this point I may or may not have some useful information--- then I would proceed to:

    3) Pull chassis and perform a visual inspection of amp circuitry---- including age/condition of output/preamp tube sockets (general soldering, possible carbon arcing, tension of contacts), bias circuit components (special attention to Bias Cap--- measure resistors), screen grid resistors (inspect condition/measure).

    4) Pull doghouse cover and inspect Filter caps and dropping resistors.

    Depending on the outcome of this work I would probably have enough information to proceed in a logical manner to properly service the BF Vibrolux Reverb and return it to being a great sounding amp.
    If the owner was in my shop during this work, he or she would be able to play through my BF Vibrolux (replica) that everybody seems to love the sound of:

    [​IMG]

    Trying to troubleshoot tube amps online is a very inaccurate way of going about returning troubled amps to proper operating condition---- if amp troubleshooting is beyond your current abilities then it just makes sense to take the amp to a tech that you trust................... gldtp99
     
    Last edited: Feb 1, 2015
  13. DGDGBD

    DGDGBD Member

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    I wouldn't mess around...just bring it for service. Not worth guinea-pigging your amp repair skills on a nice vintage piece like that.
     
  14. swiveltung

    swiveltung Member

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    The ultraviolet/blue is normal.... at least some times.
    Try different output tubes.
    Also, look at the screen resistors on the power tube sockets for overheating or being broken.
    Have you checked the bias?
    As mentioned, what is the condition of the Filter caps? Original? blistered on the ends?
    I wouldn't continue to play it, you might blow an original transformer.
     
  15. mmp31

    mmp31 Member

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    Thanks for the link. I have not taken the chassis out of the cabinet yet so I don't have any measurements at the moment. It's hard for me to say if the emission is "bright" or "faint" because the terms are subjective. I can see it under normal office lighting conditions, but I don't know how it would look in the dark. I will check on both of these and report back.

    I have not, but I have done the reverse: I hooked the speaker cab up to my Vox AC15. There is no issue with the speakers in the Vibrolux.

    Yes to all.
     
  16. mmp31

    mmp31 Member

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    I appreciate that but there's no need for anyone to talk down to people who come in here.
     
  17. pdf64

    pdf64 Member

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    Is the blue emission of a similar, or lower, brightness level as the orange glow from the heaters?
    Alternatively, if outside on a bright day would it be apparent?

    Useful things to check would be the value of the 470 ohm screen grid resistors on terminal 4 of the power tubes, and the resistance of the OT primary, CT to each plate.

    Then the Vdc at terminals 3, 4 and 5 of the power tubes, the Vdc between each terminal 3 and the OT primary CT, and the Vac across the line supply and heaters.
     
  18. Kurzman

    Kurzman Supporting Member

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    "Quote:
    Originally Posted by Kurzman [​IMG]
    Op:
    I think the guys here usually want to help but advising on working on an amp is kind of a tricky thing because you can actually kill yourself messing around with these things if you don't know what you're doing.
    And the techs on this board have no way of knowing if you're able to work on a "hot"amp safely.


    I appreciate that but there's no need for anyone to talk down to people who come in here."

    You're 100% right about that.
     

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