capacitor dissipation pictures

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by metheniac, Feb 11, 2008.


  1. metheniac

    metheniac Supporting Member

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    I know this is a long shot due to the work and picture loading involved but was wondering if anyone out there is interested in posting or knows of a site that has Visual Pictures (typical amp) showing exactly where to place the clips to dissipate the cap voltage. Also, point out some of the do not touch areas inside a typical chassis.

    I have read a ton of text on this but I need to see it visually before the comfort level in me takes over and I start to poke around inside that can of worms. If I see it once then I won't feel so intimidated about working inside of the chassis especially when biasing with a pot located inside and will have a little more respect for the lethal voltages that come with the territory.

    Thanks again.
     
  2. MisterAgreeable

    MisterAgreeable Member

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    Well, there's no universal answer, unfortunately. Filter caps can be aligned all sorts of ways, or in lots of different places.

    They might be in a can mounted to the chassis like your tubes are. They might be hidden away on their own board, with a cover over them like in Fenders. In that case you just have to know which leads those are and discharge them. I have an old Peavey power amp where the filter caps are very obvious but finding a good place to discharge them is very difficult.

    What sort of amp are you planning to work on? Someone here will probably have some familiarity with it and can advise where they are and how best to discharge them.
     
  3. metheniac

    metheniac Supporting Member

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    Good point. I guess there is no typical amp setup as I originally posted but a fender deluxe silverface from the late 70's was what I would mostly be interested in.
     
  4. Steve Dallas

    Steve Dallas Supporting Member

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    Shorting filter caps is not the best way to drain them. Get a 10K 10W resistor and touch one end to ground and the other end to the (+) terminal of any of the large filter caps. The voltage will safely drain in a matter of seconds and the caps will thank you for it. Oh, and the big resistor gives you something to hold on to while you are doing it.

    Be careful!


    I usually recommend that you turn the amp on and off standby so it is making sound. Then turn it off, but leave the standby switch alone. You should hear the volume drop and fade away to nothing. At that point, there should be less than 12VDC stored in the filter caps, which is safe level.

    Then use the resistor method described above just to be sure.

    Again, be careful!
     
  5. IIIBOOMERIII

    IIIBOOMERIII Member

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    Find V1 and clip a wire from pin 1 on V1 and run
    it to the ground of the chassis. V1 is the first
    tube the signal hits coming from the guitar input.

    This works on most amps....but not early Marshalls.

    Be careful!!!! You are dealing with high voltages,
    enough voltage to stop your heart. You can die
    if not careful.

    Don't be in a rush to do this...read, read, read.

    take care,

    Eddie
     
  6. donnyjaguar

    donnyjaguar Member

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    I don't think its wise to work on any high voltage circuits unless you have a firm grasp of the rudiments. Sorry, just being honest here.
     
  7. MisterAgreeable

    MisterAgreeable Member

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    Yeah, those have the filter caps on their own board away from everything else. you'll have to find the leads coming from the power supply board.

    Things got a bit weird in the late seventies, but usually there will be four wires coming from that board. It will be an opening near the main circuit board, on the side with the controls. On the other side of that opening will be a metal cover.

    One is black, which goes straight to ground. The red one will have the highest voltage. I use a lamp with alligator clips and a probe. I guess I like seeing the lamp light up every now and then - it makes a very visible reminder that I'm dealing with real-life voltages here.

    Anyways, don't just short them out, as someone said above. You might end up with little bits of molten metal flying at you. Find something, a big resistor or a lamp (make sure the switch is on!) or whatever, and use that to dissipate the voltage.

    Do a google search for the Fender Field Guide and look at chassis layouts for deluxes. You'll see the wires marked with > 400 volts - those are the ones you want to target. Sometimes they won't have info for your exact model, but those circuits didn't change a huge amount. Like someone said above, just read up. I think it'll make sense once you start looking at diagrams.
     
  8. MisterAgreeable

    MisterAgreeable Member

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    Ok, this is a slightly different amp, but the circuits should be similar. Just be careful.

    Look here:
    http://www.qrp.pops.net/tube_amp.asp


    There seems to be something wrong with his captions, but look at the 9th picture down. This one:
    http://www.qrp.pops.net/tube_amp/Ta10.JPG

    Do you see those braided wires at the bottom? Those are coming from the power supply board. That's the far right side of the circuit board, closest to the power transformer.
     
  9. metheniac

    metheniac Supporting Member

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    Good pics to get me started on a cap job. Thanks for all of the tips guys.
     

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