unclej Posted December 26, 2004 Report Share Posted December 26, 2004 i'm replacing all of the caps in the alamo bass amp that i've been working on. one of the power tubes has a big ole honkin' wire wound that has no markings on it at all. without the schematic (which i still haven't found) how would you know what to replace it with? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 27, 2004 Report Share Posted December 27, 2004 Uh..., if it's wirewound, it isn't a cap - it's probably a resistor. Quote Link to comment Share on other sites More sharing options...
JohnnyG Posted December 27, 2004 Report Share Posted December 27, 2004 like lovekraft said that'll be a resistor not a cap. its that size because it'll be for biasing the power tubes and so will need to deal with alot of power. i would have thought a wire wound would be fine to keep and wouldnt change value much but im happy to be proven wrong lol Quote Link to comment Share on other sites More sharing options...
unclej Posted December 27, 2004 Author Report Share Posted December 27, 2004 ooops..ok, nevermind Quote Link to comment Share on other sites More sharing options...
perhellion Posted December 28, 2004 Report Share Posted December 28, 2004 Good question, though. If it is an unknown cap, what do you do? I know all the colors and stripes can be "decoded", but what if it is in something from another era and say the Ukraine, and the colors are all different. And, of course, no scematic available. Quote Link to comment Share on other sites More sharing options...
crafty Posted December 28, 2004 Report Share Posted December 28, 2004 capacitors don't have colors or stripes... Quote Link to comment Share on other sites More sharing options...
Daniel Sorbera Posted December 28, 2004 Report Share Posted December 28, 2004 (edited) resistors are the only things that have the colored strips that you can decode. caps should have a value printed on it. Edited December 29, 2004 by Godin SD Quote Link to comment Share on other sites More sharing options...
Saber Posted December 28, 2004 Report Share Posted December 28, 2004 On the contrary, mon ami. Some capacitors use a color code. Check this site for reference. Quote Link to comment Share on other sites More sharing options...
unclej Posted December 28, 2004 Author Report Share Posted December 28, 2004 oh boy...FOOD FIGHT!!! Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 28, 2004 Report Share Posted December 28, 2004 No need to fight - limited experience makes for hasty answers, but if you guys will google "tropical fish caps", you'll understand what Perhelion and Saber are talking about - especially in an amp as old as UncleJ's Alamo, color-coded caps were quite common. Quote Link to comment Share on other sites More sharing options...
perhellion Posted December 29, 2004 Report Share Posted December 29, 2004 What I meant was, given an unknown cap, how do you tell what it is? I understand there is a meter to check capacitance, but an old cap may not correspond to color codes or may not have legible markings on it. Combine this with the possibility of the old cap no longer performing up to snuff, and I don't see how one tells what the value of the old cap is. Put another way, if you are given an old cap with no writing or colors that you can determine anything by, how do you find its original value? Quote Link to comment Share on other sites More sharing options...
panday44 Posted December 29, 2004 Report Share Posted December 29, 2004 MEASURE IT BY A TESTER.... THERE'S A MULTI TESTER THAT HAS A CAPACITANCE... OR IN OHMETER.. IF THE METER FLANKS ONCE THAT IS CAPACITOR... Quote Link to comment Share on other sites More sharing options...
Daniel Sorbera Posted December 29, 2004 Report Share Posted December 29, 2004 ya but he said it's is fried. Will it still tell you it's original value? Quote Link to comment Share on other sites More sharing options...
lovekraft Posted December 29, 2004 Report Share Posted December 29, 2004 ...if you are given an old cap with no writing or colors that you can determine anything by, how do you find its original value? If you don't have a schematic, you'll have to guess, based on what the cap does (coupling cap, cathode bypass, power supply filter, etc.), and how it fits into the rest of the circuit (context is everything) - for instance, if you're familiar with classic Fender amps, you can probably guess correctly about power cap values because the power supplies are so similar, and coupling, cathode bypass and tone stack caps can be adjusted to personal taste. In general, the only caps that drift badly or fail with age are tantalums, paper/oil and electrolytics - ceramics and micas (and film caps, but you don't find them in old amps) are pretty stable, so unless they're obviously dead, replacement is usually elective. Quote Link to comment Share on other sites More sharing options...
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