Here are dog-bone resistor size comparison pictures with contemporary resistors and wattages from my website:
http://www.philcorepairbench.com/resistcompare.htm
Chuck
:Here are dog-bone resistor size comparison pictures with contemporary resistors and wattages from my website:
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:http://www.philcorepairbench.com/resistcompare.htm
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:Chuck
High temperature and even moderate temperature is what ruins a carbon composition resistor. The carbon content spreads and separates microscopically, which can raise the resistance as high as imaginable (millions of ohms sometimes, or so high that it seems as though the resistor is open--sometimes it is). Carbon film resistors do not drift usually, as the film is solidly adhered to the resistor form's edge (usually ceramic or bakelite). They do not look original in radios, but in many ways are superior electrically. Not drifting is a large plus. Antique Electronic Supply says that carbon composition resistors can handle pulse currents better, however, which I think has to do with the resistor being a solid carbon chunk instead of a thin film. I imagine that the thin film cannot handle pulse currents as well. Radios do not usually have "pulse" currents, however, so you may use either type of resistor. If you have the time and ingenuity, you may mold bakelite (J-B Weld) around the new carbon film type resistors and make up a resistor that looks old (paint it appropriately, too), but functions with the new and improved low drift features. There is a source that people talk about occasionally on here that will make these old looking resistors for you. They are more expensive, of course, than simply ordering ordinary resistors of any type.
Thomas
:To answer your other question, yes it is normal for carbon composition resistors to drift high in value. The ceramic ones don't as often (these are the ones shown lower in Chuck's pictures--lead formed ends instead of twisted wire). The ceramic ones are often baked at a high temperature to begin with, for stability (the ones made by Clarostat). They are baked to a predetermined temperature so that they are not drifted into oblivion. Baking them drifts them initially, if they are going to drift at all. This drifted value is then the final value. This is sort of like preshrinking pants at the factory. Most companies don't preshrink pants anymore since they are mostly slave labor, and so your pants shrink after only a few washings. 60% poly-40% wool is a great alternative to cotton pants that shrink, by the way. After three years my pants have never shrunk.
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:High temperature and even moderate temperature is what ruins a carbon composition resistor. The carbon content spreads and separates microscopically, which can raise the resistance as high as imaginable (millions of ohms sometimes, or so high that it seems as though the resistor is open--sometimes it is). Carbon film resistors do not drift usually, as the film is solidly adhered to the resistor form's edge (usually ceramic or bakelite). They do not look original in radios, but in many ways are superior electrically. Not drifting is a large plus. Antique Electronic Supply says that carbon composition resistors can handle pulse currents better, however, which I think has to do with the resistor being a solid carbon chunk instead of a thin film. I imagine that the thin film cannot handle pulse currents as well. Radios do not usually have "pulse" currents, however, so you may use either type of resistor. If you have the time and ingenuity, you may mold bakelite (J-B Weld) around the new carbon film type resistors and make up a resistor that looks old (paint it appropriately, too), but functions with the new and improved low drift features. There is a source that people talk about occasionally on here that will make these old looking resistors for you. They are more expensive, of course, than simply ordering ordinary resistors of any type.
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:Thomas
At any rate, regardless of what I said, it seems that you have found an appropriate replacement resistor. I was simply explaining why resistors drift and why it is normal for most carbon composition resistors to drift.
Thomas
MILTON V.
:Well, I was talking about BOTH types of resistors. They type of resistor with the wire wrapped around the ends is usually a CARBON COMPOSITION resistor. Reread what I wrote very slowly. I talked about your resistor, another resistor pictured in Chuck's page that is similar to your resistor, but different in construction. I talked about the more modern carbon comp. resistors with the color bands, and I also talked about carbon film resistors, which are the ones currently used in most electrical devices. They have two bumps, one at each end.
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:At any rate, regardless of what I said, it seems that you have found an appropriate replacement resistor. I was simply explaining why resistors drift and why it is normal for most carbon composition resistors to drift.
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:Thomas
Thomas
:Ah. Sometimes I write so much that it can make your eyes go crossed. Glad you got it all. If you didn't, though, I understand. Sometimes my eyes go crossed when I read my own writing. Also, just a note: when I capitalize words, I usually do it for clarification. I realize that in the internet age people take all caps as shouting, but that is not how I intend it. Since I write so much sometimes, I must emphasize key words to minimize confusion. After reading carbon this and carbon that a hundred times, it can all be very confusing.
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:Thomas