Ceramic Cap Value Frustration

Discussion in 'Amp Tech Center' started by ArcticWhite, May 17, 2019 at 7:33 PM.

  1. ArcticWhite

    ArcticWhite Tele-Meister

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    Gah, I still have trouble figuring out small cap values.

    I pulled this ceramic cap from a 50 year old amp. It is marked "500".

    Is that its cap code, making it a 50pf cap?

    Or is it a 500 pf cap, plainly marked?

    If it was marked 501, then I guess it would be a 500pf?

    20190517_162804.jpg


    Now, how about this one - marked 1700?

    20190517_162813.jpg

    I can read these if they have a last number that isn't zero. 472, 501, etc.

    But the ones ending in zero mess with my head.
     
  2. BILL-NOW

    BILL-NOW TDPRI Member

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    Probably 500 pf and 4700 pf.
     
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  3. kbold

    kbold Tele-Meister Silver Supporter

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    The last digit of a 3 digit number code is the 10's multiplier.
    The first 2 digits are the capacitance in picofarads.
    So the first cap is 50pF (50 x 10^0)

    The second cap is not standard marking. The 4th digit isn't a tolerance code (the tolerance is printed below). At a guess, they printed the actual value (in pF) on the casing, having the room to do so due to the caps larger size.
    So the second cap would be 4700pF.
     
  4. ArcticWhite

    ArcticWhite Tele-Meister

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    That is true, largely, but this is a 500pf cap. I checked the schematic and that's what it is.
    I guess they only used the multiplier if it was 1 or above.
     
  5. kbold

    kbold Tele-Meister Silver Supporter

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    If that's the case, I'd guess both caps are not using standard markings, and are just labelled with their picofarad values.

    Or possibly ..... the first cap looks relatively newer.
    It may have been replaced. i.e the specified 500pF was replaced with a 50pF ??

    Stranger things have happened.
    Perhaps measure the caps with a multimeter that can measure capacitance.

    My guess is that both original caps in the amp did not have caps with standard codes, and the original cap labelled 500 (actually a 500pF) was replaced with a 50pF cap.
     
    Last edited: May 17, 2019 at 10:06 PM
  6. howardlo

    howardlo Tele-Holic

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    Test it with your multimeter and see what it reads.
     
  7. schmee

    schmee Poster Extraordinaire

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    The "500" is typically 500 PF. Pretty common on those low value small caps. For instance, the 250 PF common in Fender BF/SF amps is just marked "250"
    Is it possible the 244 is the cap code on the other one instead of the 1700?
     
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  8. kbold

    kbold Tele-Meister Silver Supporter

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    The 1 in 1700 is actually a smudged 4, so 4700.
    The 244 may be a date or manufacturing code.
     
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