bypass & filter capacitor type

Discussion in 'Amp Central Station' started by cottontails1959, Aug 26, 2020.

  1. cottontails1959

    cottontails1959 TDPRI Member

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    Quick question - cost considerations aside, can metalized polypropylene caps be used in place of electrolytic caps of the same capacitance and voltage rating as cathode bypass or filter caps in a guitar amp circuit?
     
  2. printer2

    printer2 Poster Extraordinaire

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    Sure. It's only money once.
     
  3. Paul G.

    Paul G. Friend of Leo's

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    An electrolytic cap will offer high capacitance, high voltage and compact size. If you can find a poly cap that meets the capacitance and voltage you need, and will fit in your space, well electrons don't care where they hang out.
     
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  4. cottontails1959

    cottontails1959 TDPRI Member

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    I'm trying to organize my first ever component order, and selections are overwhelming. I can see electrolytics seem to be the way to go for >20mf and a lot of choices <0.01mf ... it's the choices of those sizes in between that have me :confused: preplexed what to choose; and I'd like to not have to worry about polarity. I'm not tone sniffing, I just want reliable components ... admittedly, small electrolytics remind me of chihuahuas of the dog world :rolleyes:

    FWIW, I've done enough DYI home wiring and fixture installation to not assume that things rated the same work the same. In the vein of Ronny Regan ... "trust, but verify"
     
  5. gusfinley

    gusfinley Tele-Afflicted

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    I haven't followed them for a few years, but when I did Carr Amplifiers where built with Poly Filter caps. In Theory, they should never need cap replacements. I've looked into them somewhat, they are usually a larger size as more expensive.

    There are also non-polarized Electrolytics available. I have purchased some of these in cathode bypass cap size. I'm not if they make them in Filter Cap spec range.
     
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  6. gusfinley

    gusfinley Tele-Afflicted

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    I checked a few online suppliers and it seems like Film Caps are available in the 400 to 600VDC range in values up to 25uF and not much more (For Axial Types). They seem to run around $10USD for the larger values and seem to be about 1.5" in diameter and 2.5" long.

    It Seems like these could work in some of our amps, perhaps with slightly modified layouts.
     
  7. Switchy

    Switchy Tele-Afflicted

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    It's true that you can substitute components, but my philosophy is, there's a reason one a particular style of capacitor was used for a specific application.
    I'd recommend using the same style whenever possible, even if it's just for the sake of aesthetics.
    For larger values you will eventually have to use electrolytics and such.
     
  8. gusfinley

    gusfinley Tele-Afflicted

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    Sometimes that reason is because the manufacturere was cheap and was looking for a part that was good enough to last until the warranty period is done. Sometimes this works out tonally but other times it leads to poor quality.

    With Electrolytics caps not passing the guitar signal on to the next component and being a High-Fail (Expected Fail, ticking timebomb) component, improvements should be welcome!
     
  9. tubegeek

    tubegeek Friend of Leo's

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    1) open a discarded air conditioner
    2) remove the 2-section motor run cap (typically 35 & 5 uF @ very high voltage, high quality unkillable film cap)
    3) use in a guitar amp
    4) gloat
     
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  10. hepular

    hepular Tele-Meister

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    just have to fight off the tweakers going for the copper tubing . . .
     
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  11. Switchy

    Switchy Tele-Afflicted

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    Hate to be a buzzkill, but the capacitor in my AC died after 17 years. :confused: Not unkillable :cry:


    35 5 91hkedIqvRL._SL1500_.jpg
     
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  12. tubegeek

    tubegeek Friend of Leo's

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    There's always the .05% outlier!
     
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  13. hepular

    hepular Tele-Meister

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    now aside from the fact that a 75 mf 250v poly cap is like 10x more expensive than the 68mf 100v e-caps i replaced the neg bais caps in my super champ with . . . how would installing non-polarized caps in something where the polarity seems to make a difference work?
     
  14. tubegeek

    tubegeek Friend of Leo's

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    It only makes a difference in a part where it makes a difference TO THE PART. Electrolytics must go the right way because of the electrolyte chemistry. Film caps have no such limitation. If you want to get tweaky you can distinguish the outer foil but it's not necessary. The A/C parts are grounded to the can, you don't get a choice on those, but if you had a positive common, and insulated the can, they'd work fine "upside down."
     
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  15. avspecialist

    avspecialist Tele-Meister

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    For me, I would stay with the electrolytic’s, like F&T and I find the tone of Mojotone Vitamin T, paper in oil caps to have a really nice sound, very smooth and warm sounding in my 60’s style Fender builds. I rebuilt 2 Silver Faced Fender Twins, same speakers and tubes, 1 with the Mojotone caps and the other with Orangedrops, and friends of mine always comment on the the smooth and big sound of the one rebuilt with the Mojotone caps. I don’t tell them what’s inside, cause i’m looking to get an honest opinion.
     
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