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Thread: Stocked Capacitors

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    Member E biddy's Avatar
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    Stocked Capacitors

    I'm trying to put together a selection of capacitors that I should have on hand to work on Fender type tube guitar amps. This is what I have so far;

    Power Supply: 22uF 500v Electrolytic

    Cathode bypass: 25uF 50v Electrolytic

    Tone Stack and tone Shaping:

    10pF, 25pF, 120pF, 250pF (Ceramic or Silver Mica?)

    3nF, 47nF, 100nF (Ceramic or Polyester?)

    Coupling Caps: .1uF (Polyester or Polypropolene?)

    Any suggestions of what should I add to my order.

    Thanks

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    Don't forget the joker g1's Avatar
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    Bias filter caps. I generally use 100uF/100V, others may offer alternative values.

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Member E biddy's Avatar
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    Any other ideas. I have trouble believing that I could have gotten it that right!

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    Old Timer Leo_Gnardo's Avatar
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    To work on some of Fender's newer amps - "new" in the last quarter century more or less - I'd add 0.022 uF aka 22 nF 630 polyester or polypro, and 47 uF 500v electrolytic. Some of the 60's-70's classics used as their main hi voltage filters stacked 70 uF 300 or 350v, those are a bit hard to find so I'd suggest 100 uF 350V, and if you feel like beefing up those power supplies use 220 uF 350V.

    Sometimes you run across an amp that turns out parasitic ultrasonic oscillations. Sometimes Fender took a swing at damping them with 47 pF across the drive tube plates. But sometimes it takes up to 470 pF to thoroughly put those pesky parasitics out of our misery. The lowest value used, the better. I'd recommend having a collection of 1000V disc caps for this purpose 47, 100, 220, 330 & 470 pF.

    As for that 3 nF cap, found in black/silverface reverb return preamp, it's much easier to find 0.0033 uF / 3.3 nF. Rare that the old ones go bad but ... you never know. Cheap enough part to stock, but I wouldn't go overboard. Ten would probably last you a lifetime, with a few left over.

    BTW some of the old tweed amps used 22 nF as well.

    I keep in stock both Mallory 150 (now Cornell Dubilier) as well as Panasonic polypro or polyester "brown chiclet" film caps, all 630 VDC rated. Mouser, Newark aka Element 14, DigiKey all good industrial sources for the disc & film caps. Antique/CE/tubesandmore.com have the respected F&T electrolytics. If you're established as a business Magic Parts aka Ruby Tubes have good house brand electrolytics at rock bottom prices. I've used them for 20+ years, rarely had a problem.

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    Member E biddy's Avatar
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    Thanks Leo and G1!

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by E biddy View Post
    Any other ideas. I have trouble believing that I could have gotten it that right!
    I agree with g1 on bias supply caps. Axial lead, normally, though depends on the amp. Older Fender amps, they're all axial...newer PCB - based designs, they're radial lead. 47uF at the final stage is fine too....just need sufficient voltage rating, and 100V is good for all but Ampeg SVT designs.

    On cathode bypass, 22uF/100V is what I normally use. even though there's only a few volts typical across it, the higher voltage rating is a much more linear part. Nichicon TVX series on Axial, PW series on radial are good polarized parts. Their UES non-polar electrolytics are also good quality parts.

    The ceramic caps....I do like Silver Mica, but they've gotten outrageously expensive these days. NPO/COG Ceramic caps are the most stable and decent ceramic dielectrics. Single layer are larger than the multilayer NPO's, as well as the Axial parts. I've attached some data sheets that show the characteristics of the different ceramic dielectrics.

    Kemet Multilayer Ceramic Caps C317-C322.pdf
    Vishay Cera-Mite Ceramic Caps 561r.pdf
    Vishay aseries Ceramic caps.pdf
    Vishay kseries Ceramic caps.pdf
    Nichicon TVX Axial Elect.pdf
    Nichicon PW Electrolytics.pdf

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    Don't forget the joker g1's Avatar
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    Another thing is not stocking up too much on electrolytics that will not be used soon. Chuck H often posts about this and it is a valid point. Electrolytics can dry up just sitting on the shelf, so you don't want to have stock sitting around long. Just keep what you will be using regularly.
    I'm guilty of this myself, always trying to order extra stuff I might need, to justify shipping expense on the few items I need right now. So I have all kinds of stuff I will probably never use but cost me money.

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    Just because they don't have tubes doesn't mean they don't have feelings! - glebert

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    Old Timer tedmich's Avatar
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    where is capacitor in ceiling fan?
    in the spam! Nyuck Nyuck

    https://www.youtube.com/watch?v=xFkkVjiQbIs

    dig his mains cap test!

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    Member E biddy's Avatar
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    Quote Originally Posted by tedmich View Post
    where is capacitor in ceiling fan?
    in the spam! Nyuck Nyuck

    https://www.youtube.com/watch?v=xFkkVjiQbIs

    dig his mains cap test!
    That was awesome. I don't think I'm going to try it though.

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    Stray Cap DrGonz78's Avatar
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    Quote Originally Posted by g1 View Post
    Another thing is not stocking up too much on electrolytics that will not be used soon. Chuck H often posts about this and it is a valid point. Electrolytics can dry up just sitting on the shelf, so you don't want to have stock sitting around long. Just keep what you will be using regularly.
    I'm guilty of this myself, always trying to order extra stuff I might need, to justify shipping expense on the few items I need right now. So I have all kinds of stuff I will probably never use but cost me money.
    How long is too long for shelved electrolytic caps. 2 years or more?

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