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Thread: Small Black Capacitors (Kemet) on Acoustic Control Amps

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    Supporting Member TomCarlos's Avatar
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    Small Black Capacitors (Kemet) on Acoustic Control Amps

    MEF Members -

    This is yet another pre-project post for an Acoustic Control 150 Amp Head that I will repair. The question is in regards to the small black caps - I believe they are all "Kemet" brand.

    Are these caps (on both the preamp and main amp boards) tantalum type? I see that one end is flat, the other is tapered. So I assume that designates the (+) and (-) ends of the cap. The schematic also shows the (+).

    I'm guessing that most of these caps are indestructible, but that is not to be assumed. And in the event I find any that are bad, I would assume these exact replacements would be hard to find. So perhaps an electrolytic would work in their place?

    Thanks in advance for your advice,

    Tom
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    Lifetime Member Enzo's Avatar
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    Plain old electrolytics work fine.

    As to tantalums being indestructable, well, that is the LAST adjective I would apply to them. tants HATE over-voltage, and they HATE reverse voltage.

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    Education is what you're left with after you have forgotten what you have learned.

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    Supporting Member TomCarlos's Avatar
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    Good to know !! Thanks Enzo.

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    Supporting Member mozz's Avatar
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    Tantalums have lower ESR than electrolytics, so it depends where in the circuit they are used, they don't usually use them unless needed due to cost. Medical or military use them more often.

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    Lifetime Member Enzo's Avatar
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    True enough, but in these circuits, it is just a guitar amp, and I have never found a situation in which it mattered.

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    Supporting Member mozz's Avatar
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    Is this the old Acoustic control corp? I see 1974 date codes there now. I did have a Acoustic 164 that was a good Mesa clone, it was overbuilt. Maybe they got a good deal on some mil surplus parts and that's why they used them. Chances are they are fine, if not, then electrolytics would be ok to repair as long as nothing special in the circuitry, such as SMPS.

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    That was my guess, they got a good deal on them somewhere.

    Rebuilt one of those 164 Mesa clones recently.
    Pretty cool forgotten amp.

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    Supporting Member The Dude's Avatar
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    Sure you could replace them with 'lytics, but why not just test them?

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    Supporting Member TomCarlos's Avatar
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    Yes, they will be tested using the Atlas ESR70 Equivalent Series Resistance Meter and I will measure voltages on both ends. But, for now, I wanted to know what I am working with!

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