Capacitor: one value on cap, different to board???

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by mcdes, Feb 15, 2012.

  1. mcdes

    mcdes Member of no importance

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    I have a new amp arriving next week, so I've got my ac30 taking a sabbatical....

    So in the meantime, for work, as an electrician, I've been looking at power factor/capacitors Yada Yada.....

    So to better get to know the basics, I'm changing the caps in my heritage vox ac30.

    So I'm starting with the filter caps. They have Trec ones in there at the moment, and I've swapped for F&T. The old value was 47uF, and so I've put that back in. The schem seems to say this too, but on the circuit board itself, it says 10uF! Wha!!!

    So do I follow like with like? Or CB??

    I pulled open a Trec to see if it didn't have a different value inside, just incase! Ha, but it was all cap.

    Also, does it matter if the outer casing touches another resistor beside it etc??

    Any and all help is welcome!!

    I just spent a week going through all pages in the info section!!! Good reading! Ha
     
  2. eddy999

    eddy999 Member

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    Go with the schematic, especially as the old value you had in there matches that. You've not mentioned the voltage handling of the cap - I assume you at least matched the handling of the old one.

    As long as it's just the plastic/outer shell touching then that's most likely fine. Ideally you'd like a little gap in there in the case where the resistor is getting hot/dissipating a fair bit of power, but it's most likely not going to be a problem.
     
  3. vibrostrat43

    vibrostrat43 Supporting Member

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    Go with the schematic, I've heard of boards sometimes having misprints due to a company using extra ones from another model with the same layout, but somewhat different parts values.

    Also if it's either the mains filter, or the screen filter as I suspect it is then 47uf for this particular amp is much better than 10uf which would likely not filter the modulating DC enough and your guitar would sound out of tune when cranked up (more likely to happen if it was the mains filter at 10uf than the screen).
     
  4. mcdes

    mcdes Member of no importance

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    Yea, I went from 350v to 500v on the new ones.

    The new F&T ones are bigger than the old ones! So I mounted them
    Kinda up off the turrets a bit more to give clearance, so now there is a few mm's gap in there.

    Gonna go through and just touch solder when I'm finished too. I just touched the ground, screen grid resistor (whatever it is) from the top boost volume pot and it fell off! Gee wiz!
     
  5. mcdes

    mcdes Member of no importance

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    Hahaha, and funniest thing! Changed three caps, decided to test it before moving on....... Just incase it was wrong.

    ......Didn't work.... Packed myself!........ Oh right! Bad instrument lead.... Resoldered... Phew!! Haha
     
  6. TweeDLX

    TweeDLX Member

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    You can put a blob of high temp silicone between the caps to keep them stable.
     
  7. mcdes

    mcdes Member of no importance

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    I've never heard nor seen that! But that sounds like a great idea!
     
  8. mcdes

    mcdes Member of no importance

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    Another question??

    I have three caps, one is 25uF/25v, and another two are 22uF/25v.

    Will it matter if I make them all 25uF/25v??
     
  9. Ronsonic

    Ronsonic Member

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    Cap tolerances are such it doesn't much matter which you use.
     
  10. mcdes

    mcdes Member of no importance

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    so ive changed them over, filters to F&T's, and signals to Sozo's. sounds friggen great so far!

    thanks again for the help....... next up, resistors and trannies!
     
  11. neteraser

    neteraser Member

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    Hahaha! I like people like that.
     
  12. donnyjaguar

    donnyjaguar Member

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    I think you'll find most electrolytic capacitors measure higher than their label. I believe this is because as they get hot the value drops. So if they're rated at 85°C then at that temperature they should be the correct value.

    don't burn your fingers.
     

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