Filter capacitor replacement question

Discussion in 'The Workbench' started by Gutch220, Jan 22, 2021.

  1. Gutch220

    Gutch220 Well-Known Member

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    If the original filter cap has 4 'legs' for wiring is being replaced, but the new ones have 3 'legs', is there a way around this to make it work? Would you need a schematic?

    upload_2021-1-22_18-50-6.png




    ???
     
    Last edited: Jan 22, 2021
  2. thetragichero

    thetragichero Well-Known Member

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    what does the side of the cap say? how many sections?
     
  3. South Park

    South Park Well-Known Member

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    As long as the ground is hooked up right . You can double up on one connection . It may not have all the filtering but worth a try
     
  4. Gutch220

    Gutch220 Well-Known Member

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    can you explain to me how the sections "work"? I assume one leg is ground, and the other two legs are 'capacitance'? so a 3-legged cap would have 2 sections and a ground?
     
  5. 2L man

    2L man Member

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    Capacitors don't have grounds! Circuit defines the ground and signal ground and chassis/shield are electrically different items although they usually are connected together!

    You need to find how new and otiginal electrolyt are constructed.

    Modern can electrolyts often have third contact which is the actual outer can and it can be used as a shield so connect it to chassis and positive and negative eletrodes like original is connected.

    When outer can is separate from other electrodes it makes capacitor more versatile to use when negative can have different voltage level what signal ground has. Also signal ground and shield/chassis stay separate and no ground loops form.

    Some can capacitors can have parallel pins although there is only one capacitor in it and it is because they can release so much current that only one pin ot where it is soldered fails.

    Often can has heat shrink and you can strip it away where the mounting band comes and it connect chassis to capacitor and come to same shield. Size of a finger nail should be enough.

    I have read that aluminium and steel mounting band form an electrical pair which oxidises contact layer eventually but obviously it still works and "shorts" high frequenzy electromagnetic noise? If can has a pin which takes solder you can use a wire between it and amp chassis but then do not remove heat shring insulation to avoid ground loop.

    This came awful bubbly explanation but I tried to make it clear enough that no (other knit picker) traditionists need to comment nonsense ;)
     
    Last edited: Jan 23, 2021
  6. Gutch220

    Gutch220 Well-Known Member

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    I don't think there's any way I can find out how the old one was constructed, how a new one would be constructed or if/how I could replace the 4-legged one with the 3-legged one, and just double-up on one of the legs.
     
  7. 2L man

    2L man Member

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    Does original have two or three capacitors in same can?
     
  8. 2L man

    2L man Member

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    If it has two, three or even four independent capacitors usually there are resistors between contacts and they are positive descending voltages to difgerent amp stages. Resistors can be also elsewhere.
     
  9. 2L man

    2L man Member

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    I see four contacts and obviously one of them has internal contact with the can. How you knew what kind of replacement you bought?
     
  10. 2L man

    2L man Member

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    There should be letters or numbers on contact bases. They often are rivets and when they are pressed the tool leaves a mark and they should be written to heat shrink. Other marking I know is on insulation next to contacts. If neither then you need to visit manufacturer database?
     
  11. thetragichero

    thetragichero Well-Known Member

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    the side of the old can cap should have either a key (maybe with symbols) or at least mention what the sections are
     
  12. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    How about finding the schematic for that amp? It should tell you all you need to know.
     
  13. Gutch220

    Gutch220 Well-Known Member

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    I didn't buy anything. This is an issue with a person I know, but I'm asking because I'm interested for my own knowledge.

    This is the schematic
    upload_2021-1-23_14-30-49.png



    Here is a close-up of the cap. As mentioned, it looks like, on the rivet, it says "A"...."B"......"C"......and "I".
    Perhaps this can help in determining if a 3-legged cap could replace the 4-legged cap.
    upload_2021-1-23_14-34-43.png
     
  14. thetragichero

    thetragichero Well-Known Member

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    what's the side say? there should be a key. most likely I is common. i would assume this to be a 3-section cap
     
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  15. Gutch220

    Gutch220 Well-Known Member

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    does a 3-section cap have 4 legs?

    I will check the side, now.
     
  16. thetragichero

    thetragichero Well-Known Member

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    3 section cap has 4 terminals. one for each section plus a common terminal
     
  17. Gutch220

    Gutch220 Well-Known Member

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    There are three caps; two large ones with 3-legs, and one smaller cap with 4-legs.

    The two larger caps are labeled 50uFx2 500v - com neg (see photo) so these are the 3-legged caps. Are the 2 non-common legs identical?
    upload_2021-1-23_15-21-13.png

    The one smaller cap is labeled 20uFx3 450v -Com Neg (so this is obviously 4-legged). Does this mean the other non-common legs are identical?

    Again, I'm trying to see if it's possible to replace a 4-legged cap with a new 3-legged cap. I will try to get an image of the bottom of the new capacitor.
    upload_2021-1-23_15-24-11.png


    thanks
     
  18. thetragichero

    thetragichero Well-Known Member

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    yes each 50uf section is identical and each 20uf be section is identical
    sure, you can replace a 3 section can with a 2 section can, but then you've gotta add another capacitor somewhere

    https://www.tubesandmore.com/products/capacitor-jj-electronics-500v-5050-f-electrolytic will work for the 50/50 cans although they may take a different clamp size

    https://www.tubesandmore.com/products/capacitor-jj-electronics-500v-40202020-f-electrolytic would work for the 20/20/20. you'll have an extra 40uf section. it's possible we could find a use for it. they carry 20/20/20 caps but they're 38 bucks so the only time is spring for them would be a vintage amp (I've used the ce manufacturing caps in a 68 vibrochamp and 69 sceptre)
     
    Last edited: Jan 23, 2021
  19. Travis398

    Travis398 Well-Known Member

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    No... You need 3 sections or add another one as suggested
     
  20. Gutch220

    Gutch220 Well-Known Member

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    so it's OK to leave the extra 40uF leg disconnected to anything?

    in the underlined section above, when you say you'd need to add another capacitor somewhere, what would happen if you just 'doubled-up' on one of the 20uF legs?

    thanks
     

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