Tube Amps / Music Electronics
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|6/2/2004 11:17 PM|
|gene huss||1954 Fender mystery|
working on a 54 Fender Pro-amp.I have a question about a strange looking part inside.It appears to be a cap-it looks exactly and shaped like a domino with six colored spots on it.The spots are one white,one green ,and 4 black.
I did hook up a cap meter to it and it measures about 600pf.It is wired between the tone and inst. vol pots.
What the deal with this ancient part???
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|6/2/2004 11:53 PM|
Those are mica caps.
There are few schemes to read the codes.
Somewhere on the front will be either an arrow covering a whole row, or maybe little arrow marks next to the dots on one row. In any case, the arrows should point to the right and the dots read right to left. Two rows of three.
In the case of the top row has three little arrowheads, the dots are:
Top row - type, first digit, second digit.
Bottom row - class, tolerance, multiplier.
two digits and multiplier read in picofarads - in those days picofarads were called micro-microfarads or mmf.
Voltage rating is color x 100. So brown, red, yellow mean 100, 200, 300 respectively, and so on.
In the ones with an arrow enclosing the whole top or bottom row, the row with the arrow is the value. ANd it reads first digit, second digits, multiplier. The non-arrow row reads - voltage, no color, tolerance.
The colors can fool you at this age. Blues can look like black, so can browns. Even reds can dull to brown or black.
Colors mean the same as for resistors for value. VOltage I mentioned. For tolerance, silver means 10%, no color (color same as body of cap) means 20%. (20% parts were the norm back then) Though unusual, brown through white tolerance was 1-9%.
ANd for your info, if you run into the old paper caps or film caps in the plastic axial lead, the color stripes can be read the same way. Like a resistor but in picofarads. two digits, multiplier, tolerance, two bands for voltage.
|6/3/2004 5:47 PM|
Thanks Enzo.Im a little lost still,so i will explain the cap better.
the top row of dots reads: white green black, left to right.
the bottom row reads; brown black brown ,left to right
the top dots: each dot on top row is surrounded by its own arrow that points to the right (3 arrows total)
Bottom row has no arrows.
So, what would the actual value be ??
|6/3/2004 6:00 PM|
according to the scem i just found, its a .005 cap.
|6/3/2004 10:50 PM|
You have the three arrow type per my other post, so your second and third dots are the first two digits, and the lower right is the multiplier, so like the man said, you have a 500pf cap. 600pf is within 20%, and that is not bad considering age. Micas are a lot less likely to get leaky than papers.
|6/7/2004 4:13 PM|
This is not necessarily a mica cap. Many paper caps were mfg'd in this era which are encased & coded the same way, especially if they are on the somewhat larger side, and they are all cheap crap that are almost always leaky, I have replaced many.
|6/7/2004 11:30 PM|
If he had a .1 or something I might agree, but I doubt a 500pf is paper. I still vote mica.
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