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In Reply to: color coded capacitors/Scott 121a preamp posted by blackbart on March 8, 2003 at 15:06:38:
Hi - I'll try to describe it in words because right now I'm at a computer with a very slow connection and I can't really search for the code chart jpeg.Look at or hold the cap so that the bands are bunched on the left.
Let's use this as the key: (n)(n)(m)(t)--(v)The first two bands are numerical indicators, with the same color designations as on resistors, i.e., 0black 1brown 2red 3orange 4yellow 5green 6blue 7violet 8grey 9white. So if it's yellow-violet it's 47, orange-orange=33, etc.
The next band is a picoFarad multiplier indicator, with the corresponding color determining the exponent. If it's red, it means 10 to the exponent 2 or 100 pF, which is then multiplied by the value from the first two bands. Orange is 10^3, yellow is 10^4, etc.
The next band is a tolerance indicator, I think black is + or - 20%, and white is 10%, I'm not sure because I don't have the chart handy and I don't think the colors correspond numerically on this band...
There's usually a gap and then the last band indicates voltage rating, with the color once again representing a multiplier of 100V, so blue = 600V, yellow = 400V, etc.
So for an example, one very coveted value is:
red-red-orange-black--yellow
... which means 22 x 10^3 pF, or .022 microFarads, 20% tolerance, rated for 400V.
These are known as "Bumblebees", made by Sprague in the 50's, and this value is found in the tone circuits of the some of most valuable guitars on the planet: '58 - '60 Gibson Les Paul sunburst models. These caps (with these exact values) can go for big coin - even in used condition - because guys are either looking to restore vintage guitars or make their current-production reissues sound and look closer to the originals. Bees of many values are also common in Marantz and McIntosh HiFi gear of the same era, and apparently Scott, too.
I've heard reports that these caps can dry out or leak their impregnant. Their capacitance values tend to drift upwards, and in critical coupling positions they can leak DC to the next stage, which is generally not healthy, so perhaps 40+ yrs later they're best suited for passive positions... like the treble bleed circuit in a guitar.
Interestingly, the Bumblebee's successor, the Black Beauty (still black axial molded plastic case, but with red, orange, or yellow writing and usually no solder-bead) is reported to be more reliable and stable - maybe due to a better seal, or maybe because Sprague had made the move to a hybrid dielectric (paper and Mylar - 'DiFilm'). I see these in pics of the guts of McIntoshes too, perhaps installed during manufacture because the amp was made sometime around the switch, or perhaps as replacement parts.
cheers
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Follow Ups
- Re: color coded capacitors/Scott 121a preamp - saros141 19:18:38 03/09/03 (1)
- Re: color coded capacitors/Scott 121a preamp - blackbart 21:11:17 03/09/03 (0)
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