Blew a filter cap need advice or info

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jh45gun, Apr 25, 2008.

  1. jh45gun

    jh45gun Member

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    OK I finished up my Super 5f4 build today and I was having problems with the bias circuit I had to build for it I figured that out and had -40 to -50 V DC so finished wireing up the last couple wires I needed to finish which was the wire from the Recifier pin 8 to the standby switch and the wire from the circuit I made for the bias voltage to where it goes on the board. Now the board I bought pre- loaded and the guy leaves the ground wires bare. I did not need to dress them in my last build had plenty of room so I did not on this one either which was a mistake as the ground wire for the filter cap which is the left one of the three 16 MFD caps blew out the side of the cap after I fired up the amp. After looking I saw that the ground wire for that cap connection had moved against my input jacks and was touching the positive prong of the input jack which shorted out the cap. So tomorrow I will go get a cap from my tech friend and wire it in and hopefully all will be ok. So do you guys think the cap took the brunt of the damage? every thing else looks ok. Oh and I dressed the rest of the wires to make sure nothing shorts out again.
     
  2. SatelliteAmps

    SatelliteAmps Member

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    Probably took most of the damage.
     
  3. jh45gun

    jh45gun Member

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    Thanks Adam I hope so I am going to my tech friend this morning for an other cap and hopefully get the amp up and running.
     
  4. jh45gun

    jh45gun Member

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    Well the cap next to that one is getting hot too though it did not blow so I shut it down after replaceing the blown cap and I guess I will have to take it to my tech so he can see what is going on. I think that when the one cap blew the other one might have been cooking too.
     
  5. jh45gun

    jh45gun Member

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    I suppose to be safe it would be wise to replace all three.
     
  6. SatelliteAmps

    SatelliteAmps Member

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    You can replace them all, it won't hurt anything. If you think it is damaged, you may also want to check the resistor in between the two caps as well (and check the one between the other ones too).
     
  7. Trout

    Trout Member

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    What strikes me as odd is it is a new build. The caps are getting hot? and they are New?

    Another thing you mentioned was the input jack made contact with the cap ground wire? If the input jack contacted the ground, it would not do anything.

    Are you certain the polarity of the caps are correct?

    Something sounds out of wack for sure.
     
  8. jh45gun

    jh45gun Member

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    Well the board is wired right and I did not do it I bought it Pre loaded from Watts Audio. Not saying I could have made a wireing mistake hooking it up but this is my second build and the first one went fine as I always double checked my wireing as I went along though I suppose I could have made a mistake though I do not see where. The PT and OT are used but both are known to be working the I checked the PT voltage before using it and I bought the OT from a music store who said it was working when they scrapped the amp. So your telling me if the ground was touching the positive lug of the input jack it would not short anything out???? If worse comes to worse I will take it to my tech and let him look at it as some times a fresh view can see a mistake you may miss. Like I said the ground wire was touching the positive side of the input jack I would think that would cause a short? The only other thing different is I had to make a bias circuit but I did with a pot in the circuit and it measured -40 to -50 v when it put it in so that should be in range.
     
  9. Trout

    Trout Member

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    Input jacks default to ground when no guitar is plugged in. Now had it touched the B+ side, I suspect fireworks would occur.

    Take a good look at the caps, There were a lot of spragues going around recently with the heat shrink on backwards.
    Take a lot at this picture,

    [​IMG]
    The positive end has a crimp on the left end in this picture regardless of the printing on the heatshrink.
    There were some pictures here on this board months back of a some spragues that were labeled backwards.

    Even if the power supply was dead shorted, the resistors, the transformer and the fuse would die. I have only seen caps blow for few specific reasons on new builds,

    Defective caps(rare)
    Reversed polarity when installed(Very Common)
    not rated for supply voltage

    The guy over at Watts does really nice work but it is possible that they are reversed or defective

    Can you post a picture?
     
  10. lannyhall

    lannyhall Member

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    I was not aware of that. I guess the visual inspection is always a good idea.
     
  11. VikingAmps

    VikingAmps Member

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    What he said. Also if you're getting more voltage than you should there it could make the cap get hot and explode. Some amp designs need the proper load on the B+ to keep the voltage under the cap's rated voltage.
     
  12. Trout

    Trout Member

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    Yep,
    I wondered about that also, I just assumed he used the correct or closely rated transformer for the 5F4 Super.

    Another thing that sort of puzzels me is why are the PS caps and or grounds at the same end of the chassis as the input jacks?
    The standard layout has them at opposite ends of the chassis.
    Original layout

    I would like to see pictures, I can tell a lot by those in most cases.
     
  13. VikingAmps

    VikingAmps Member

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    Also even if the caps + terminal shorted to ground it's not likely that it would damage the cap. It might damage whatevers before the cap tho.
     
  14. VikingAmps

    VikingAmps Member

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    Hey Trout, I used to have a U1511. You don't see too many of them around. Mine actually had the original Tung Sol 6550's in it too in great shape. Unfortunately I had a flow problem and let it go for 200. Pretty sad, huh? It made a nice bass amp.
     
  15. Trout

    Trout Member

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    $200.00?? someone got a hell of a bargain.

    Yikes!! I hope to find another one, I got mine for $8.00 minus the 6550's at a yard sale. Had a full set of Mullard preamp tubes still in it.

    These things are clean monsters, I swear its nearly impossible to stand in front of if you want any overdriven tone. I could see it working well for bass.
     
  16. jh45gun

    jh45gun Member

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    ok the tranny is rated on the origional schematic as 360 0 360. I do not know what it puts out as I tested it with out a load and of course I got a high voltage of around 460 but that is because it was not hooked up to anything and of course they will read high then. The OT is a Peavey OT that is for a 120 watt amp but I hooked it up with the 4 omn load being as 8 ohms and the 8 ohm tap being 16 ohms as I was told when you pull two tubes the ot will read different and since this amp is 2 6l6s that is what I did. The tubes are 6l6GCs and they are Winged C's I took out of a junk Peavey amp that had issues but I had the tubes checked and run under a load and the tech said they were good. OK looking at the caps the plus side is the indented side so that is right. The recifer came with the chassis and is a 5u4. The preamp tubes are all 12ax7s as when I get it up and running I will try a 12ay7 which at the moment I do not have in stock. The Choke come from Weber and is for a larger tweed amp. The input jacks are where they are because this is not a 5f4 chassis and I am making it a head build. So I laid it out as is and extended wires if I need be. The way it is on the board was the best way to put it. Excuse the poor pics my darn digital camera is going on the fritz. Fortunately I have an other but need to get a card reader for my computer as I do not have the cable for it.

    [​IMG]

    [​IMG]

    [​IMG]
     
  17. jh45gun

    jh45gun Member

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    The cap has the plus marks on the end with the crimp.
     
  18. jh45gun

    jh45gun Member

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    The caps are rated for 475 DC could it be I need a higher voltage rated cap and do they make such a thing?
     
  19. jh45gun

    jh45gun Member

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  20. TungstenAmp

    TungstenAmp Gold Supporting Member

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    Tell us more about this bias circuit. The 5F4 board that you purchased has a bias circuit to the far left, however the small board that you have installed into the lower left corner looks to be where you are drawing your bias supply from.

    Unless you disconnected the original bias circuit, I'd bet this is the source of your problem.
     

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