Tube Amps / Music Electronics
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|12/9/2002 4:52 PM|
||What color code for these values?|
I have a bunch of old circuit boards i save for parts, and many have those green body silver mica caps that look like resistors. I need the following values, but have been unable to determine with confidence what colors they'd be. So if someone could tell me what each value would be i'd appriciate it. I looked at some color code charts, but wasn't able to be 100% sure of the results, and i need to be sure i'm getting the correct values. (I am absolutly retarded where math is involved!)So if someone could give me the color codes for the following i could not only be sure, but check them against what i got from the charts to see if i'm getting the correct results. Thanks....
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|12/9/2002 9:53 PM|
I may be wrong but it could be worse than it looks.
On my surplus boards going back to the '80's, the SM caps look just the same as today's dipped micas, but the cylindrical green ones on the same boards whose bodies look like carbon composition resistors are actually inductors in the microhenry range.
Earlier SM caps were in a molded package with color-code dots that looked like dominos, but that was way before the '80's.
Unsolder one and check its resistance, a SM cap should show an open circuit, an inductor a short circuit to the DVM.
A 270pf SM may just happen to be marked in plain English with a *270 +-5%* or something like that. Without further markings you can not always assume they can handle 500V, some identical looking parts are only for 100V. Odds are that most SM are for 500V though even on a PCB that was built only to see less than 100V max. A military-type code would show that same value as 271 but that is usually buried within a longer alphanumeric sequence like CM05CD271J03 where J is the 5percent tolerance. The 271 code for 270pf would also be seen on ceramic disk and polystyrene caps, whose voltage rating should also be checked before applying tube amp levels. There may be some hollow cylindrical ceramics with color codes in the pf range, 271 would be Red, Violet, Brown but there could be more than 3 bands.
The 0.022 and 0.047 are not in the picofarad range normally covered by silver mica, the 0.022 would be a 223 and the 0.047 is coded 473. You'll see a lot of 223's and 473's on consumer circuit boards but they are usually only for 50VDC, they are nice film caps for low-voltage circuits like effect pedals.
|12/10/2002 12:10 AM|
But these aren't like that. They are color coded with rings just like a resistor, and i'm sure they're caps, as you wouldn't find so many inductors on a board. There are as many as 30 or more on some boards i have. What i need to know is what colors to look for for the values i mentioned. As for voltage, i'll just have to hope for the best. *S*
|12/10/2002 8:39 AM|
Dale, they read in picofarads. The codes are like resistor codes except it is pf instead of ohms. 270pf would be 271 - red/violet/brown. I would be mighty surprised myself if you found a .047 in one of those. We are talking the little things l;ike a quarter watt resistor or smaller right?
|12/10/2002 3:08 PM|
Thats what i thought, but had to be certain before i opened my amp amd went thru all the trouble it requires for dis-assembly. (classic 30...you know the drill *S*)
|12/11/2002 7:33 AM|
If it is a C30, just look the parts up on the schematic.
|12/11/2002 8:22 PM|
Of course, but the reason i needed the info is because i'm getting the parts from old circuit boards i have, and i needed to identify them to be sure they are the same value as on the schematic.
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