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Dumb capacitor question?


 
11/9/1998 2:01 PM
Benjamin Fargen
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Dumb capacitor question?
Can you tell me the correct replacement value in relation to the value between older caps and modern caps?  
.0005? what is the correct replacement?  
.02 ? is it .022  
.005 ? is it .0047  
 
This is a dumb one, but I just wanted to double check!  
Thanks, Benjamin
 
11/9/1998 2:28 PM
Jim S.
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Most capacitors these days are available in "decade" values, just like resitors. For 10% tolerance components, the values will be any one of {1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2} multiplied by 10 raised to some power. This scheme allows a component having ANY measured value to be labeled with the nearest decade value and still be properly within 10% tolerance.  
 
Assuming the values you listed are all in microfarads (uF), the closest decade value to .0005uF (which equals 500pF) is 470pF. However, 500pF ceramic and silver mica caps are still commonly being manufactured, so you have a choice.  
 
In general, I would say "correct" is in the ear of the beholder. It's extremely difficult to distinguish between a .02 and a .022 cap or a .047 and a .05 in a guitar amp. I find that changing a single cap's value by much less than 50% up or down doesn't affect the tone dramatically. If I'm restoring a very old amp I might want to stick with the non-decade values for general reasons of "correct vintage specs", but usually I don't sweat it if I need to replace a .003 cap with a .0033.  
 
Non-decade value film caps are also still being manufactured, but they are harder to find. The SBE (formerly Sprague) 6PS series orange drops are available in the older non-decade values such as .02uF, .025uF, .03uF, .05uf, etc.
 
 
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11/9/1998 3:09 PM
Benjamin Fargen
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Jim, Thanks so much for the help! Do you prefer ceramic or silver mica caps for the 500pf?.... or can you even tell them apart?  
Benjamin.
 
11/9/1998 5:31 PM
Jim S.
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Generally, I will upgrade to silver mica. Silver mica might be slightly less grainy sounding, but I don't think there's that much difference for guitar amp use. I doubt anyone could tell the difference in the case of the 500p coupling cap used for bleeding off the reverb drive signal in Fender amps.
 
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