'64 Super Reverb blowing fuses?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Docgab, Feb 22, 2006.

  1. Docgab

    Docgab Member

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    My nearly original (RI Jensen Speakers) '64 Super has started blowing fuses. One every few weeks. All of the tubes are good.

    When the stand-by switch is thrown there is a small amount of noise and the amp goes dead.

    Any ideas? I am worried that there is a problem in the power supply section allowing a spike or surge. Time for new filter caps?

    Thanks
     
  2. Gordon

    Gordon Silver Supporting Member

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    Hey Will,

    If the filter caps are original that's the first place I would start. They can break down to the point that they can't handle the voltage spike when you throw the standby and short out, thus blowing the fuse.

    Good Luck,

    Gordon
     
  3. Docgab

    Docgab Member

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    As far as I know they are orginal. Kind of what I was afraid of.

    Any one know where I can order kits to replace the filter caps? I have built and worked on a few tube amps. Should be pretty straight forward.:D

    Thanks.
     
  4. Reeek

    Reeek Member

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    Assuming the filter caps are located under the "ashtray" can on top of the chassis like the later Fenders, this is very easy to accomplish if you have decent knowledge. You can find the cap values on the schematic or by looking at the ORIGINAL (meaning the original caps and at spec) existing caps then just order up replacement Sprague Atoms. As you know, electrolytics are poloarized so there is a positive and negative end. if you have good soldering skills, you can just replace the ORIGINALS with the new filter caps paying VERY close attention to the polarity.

    If you don;t feel comfortable doing this, it's easy and relatively cheap to get it done at your local shop.

    One thing to keep in mind, if the filter caps are ORIGINAL, then you probably also have many caps and a few resistors inside the chassis that could use a review and/or replacement. Again, this service is vital for longevity and good measure and is not hard or expensive for most techs to do.
     
  5. Docgab

    Docgab Member

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    Thanks for the advice. Any thoughts on other brands of caps than the Sprague Atoms? How about Solens or Black Gates?

    Would they change the over all tone of the amp?
     
  6. Shea

    Shea Member

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    They won't fit, and you don't really need to spend all that money on them.

    What you need are axial lead, electrolytic capacitors.

    Solens are polyprop capacitors, which makes them way too big to fit under the pan.

    Black Gates are electrolytic, but most or all of them are radial lead caps. I guess you could rig up some way to tie them down in the pan and run leads between the terminals and the eyelets if you really want to, but it's not worth the bother or the expense.

    Vishay / Sprague TVA Atoms work well, and they're roughly about the same size as the original caps that you'll be replacing. So they'll like they belong under the pan. They've got to be at least as good as the original caps were when they were new.

    Nowadays there are other brands & makes of electrolytic caps that are a lot smaller than Sprague Atoms, for the same values & voltage ratings. Vishay / Sprague makes one or two lines of smaller-sized, axial lead electrolytic caps. Some other brands are Xicon and Nichicon. I doubt you could hear the difference if you went with one of these smaller makes instead of the Atoms, but their smaller size just looks funny in a Fender amp.

    Also, Sprague Atoms have such a good rep among guitar players that they might be better for resale value, whether or not they're actually any better than the smaller brands. No one is ever going to question the choice of Sprague Atoms, but some people are going to think, rightly or wrongly, that the smaller caps are inferior. I believe Gerald Weber once wrote that bigger caps necessarily sound better. Even if that's total BS, you can bet that a lot of guitarists are going to believe it just because he said so, and one of those guys might be interested in buying your Super one day.

    Shea
     
  7. Docgab

    Docgab Member

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    Thanks Shea.

    I guess if Sprague Atoms were good enough for Leo I should go back as close to origional as possible.
     
  8. Shea

    Shea Member

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    Leo didn't use them, but they're close to the same size as what Leo did use.

    Shea
     
  9. EXP

    EXP Member

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    it could be the transformer or you could be using the wrong kind of fuse. i had the same problem with my Super, blew fuse after fuse. turns out i was using Fast-Blow fuses instead of Slow-Blow 2 amp. ever since i switched to Slow-Blow fuses, ive had no problems.
     
  10. Docgab

    Docgab Member

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    The fuses are Slo-blo. Wouldn't a bad tranny hum?

    I forgot that Sprague Atoms are later caps. :rolleyes:
     
  11. Gordon

    Gordon Silver Supporting Member

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    You've gotten some good advice here. Sprague blue atoms are the ones that I use also and have had good success. They make a 20uf x 500 vdc that is a perfect fit inside the tray and keeps you original filtration I would also get a 25uf x 150vdc for the bias supply and replace that at the same time that you do the filters. I know that the voltage rating is higher than you need but as I remember you may not be able to get the 25uf in something lower like a 75vdc (but just relying on my memory). Mouser is a good place to buy them, fast service and good selection.
     
  12. al carmichael

    al carmichael Member

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    While I am not discounting the filter caps, my first thought was that the stand-by switch may have gone bad. When they do, they can arc inside and blow the fuse. So I would replace it in addition to doing the cap job.
     
  13. Blue Strat

    Blue Strat Member

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    It would more likely take out fuses. Worn out caps are a more likely source of hum.
     
  14. JimiB

    JimiB Member

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    sounds like you might have a bad rectifier tube to me. If its never been recaped it could sure use it, but if youve got a spare gz34 layin around try that. Also I've seen power tubes short intermitently and do that as well.
     
  15. brad347

    brad347 Member

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    yeah a bad rec tube, even an intermittent one, can take out a fuse just like that.
     
  16. VintageJon

    VintageJon Member

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    Nobody has advised the fellow to remove 6L6's and see if it blows fuse.
    If no-blow, it's a bad 6L6.

    Still blows fuse? Remove 5AR4, or what-ever rectifier you have there.
    If it now doesn't blow fuse it's likely a bad rectifier or primary filter cap.
    Replacing rectifier will tell which in this event.

    -Jon
     
  17. brad347

    brad347 Member

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    jon, that's hard when the rectifier is intermittent but not all the way down. I've had one go intermittent on me and it would only blow fuses at random times, not consistently.
     
  18. Reeek

    Reeek Member

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    I too thought about VintageJon's idea but I was reluctant because the problem was intermittent I thought. I figured that a shorted tube would blow the fuse each and every time which is my expereince many times over.
     
  19. brad347

    brad347 Member

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    i had a 5AR4 once that was dodgy and would blow fuses only occasionally. Took me forever to trace the problem...

    Also, once I had a rectifier tube that I thought was bad, but it turned out that the pins in the tube socket weren't making good contact... a little bend-action with a small pointy object and all was well!
     
  20. Docgab

    Docgab Member

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    Thanks for all of the advice. I have a few rectifiers sitting around, I'll swap them out this evening.

    The stand-by switch does have a little play in it. I may swap it out as well. I have a few spares as well.

    thanks again:D
     

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