Regarding wattage, you can find wattage charts online and at Radio Shack. You may also find them in electrical (radio and electronics) books at your local library. A good book that comes to mind which has such a chart is Alfred Morgan's "Boys' First Book of Radio and Electronics." Unfortunately most libraries have pulled his books due to so-called obsolescence. Sad. Oh well.
With wire wound resistors, wattage is determined by wire thickness among other things. Usually the wattage will be stamped upon the resistor. With resistors that are original to the radio, this may not be stamped upon them. After-market resistors--those sold at parts stores like Radio Shack and www.tubesandmore.com--will have the wattage stamped upon them.
With the old glass resistors found in early radios, the wattage capability of these is extremely small. These resistors never were meant to handle currents anyway. They were simply designed in a somewhat compact fashion for regulating control grid bias, which draws very little current, if any. Knowing the wattage of these resistors is unnecessary. Any new resistor of the same resistance (ohms) of any wattage will do.
Regarding carbon resistors, those of old design will usually have a two part color code on them along with a dot as the third color. Some will have the wire leads attached with a molded lead or bakelite end. Others will simply have the wire leads wrapped around a couple of times at the ends and then soldered in place. These resistors had their wattage classified by physical size. Any resistor with a certain width was rated to handle a certain amount of wattage. Various styles of these resistors went by different classification. If you come across these resistors (and you will quite often with 1930s and earlier radios), you will have to consult the various charts availabe for the different types. I have charts for some, but I am not sure if all of these resistors go by the same wattage-size classification.
With more modern carbon resistors, you'll find three or four colored bands for the color coding. The first two are the first two digits of the number. The third color determines the amount of zeros after the number. The fourth, if present, determines the tolerance. I'm sure you already know this color code if you've been working with radio for any length of time. I just wanted to point out this type of resistor. At any rate, the physical size of this resistor determines the wattage, and this classification system has been pretty much universally standardized. Resistors of this type from 50 years ago will go by the same classification standards as brand new resistors. You may obtain charts at the sources I listed above (Radio Shack, library, on line, www.tubesandmore.com, etc.). Here is one such web site that lists color codes and wattages:
http://www.tpub.com/content/firetrucksandequipment/TM-9-254/css/TM-9-254_217.htm
Any resistor that fits a certain size listed in this chart will be of the corresponding wattage. You will never harm a radio by installing a resistor capable of handling more wattage than the original. Wattage handling is simply the ability the resistor has to discipate heat which is generated by the current flowing through the difficult to flow through material. If you install a resistor capable of handling more wattage, it'll run cooler and last longer. Resistors which handle more wattage are generally more expensive, however, which is why radio manufacturers usually use resistors with the lowest possible wattage handling capability.
If, on the other hand, you install resistors that are not capable of handling the wattage that the originals were capable of, you may damage the new resistors. You won't likely damage the radio, though you could start a fire if the resistors heated up enough and burned something else. Also, if they burned up and took a critical load off of the power supply, the excessive voltage within the power supply could burn something else up.
Didn't mean to be too lengthy. Hope that explains everything. There are many types of resistors, so I didn't want to be too general about the whole wattage thing.
Thomas
Steve,
If you would post your email address (or email it to me) I will send you a .jpg photo that I put together in response to a similar post about resistors some months ago. This photo shows all of the comparative sizes (wattages) of resistors from 1/8 watt up to 25 watts.
Dennis
::There is no polarity to a resistor. A resistor is simply a device through which current flow is difficult. It does not matter which way the current flows through the resistor. Resistors are usually made up of material that has no polarity preference. Often this material is carbon. Wire wound resistors are the exception. Their wire is nichrome or some other metal that does not conduct current well.
::
::Regarding wattage, you can find wattage charts online and at Radio Shack. You may also find them in electrical (radio and electronics) books at your local library. A good book that comes to mind which has such a chart is Alfred Morgan's "Boys' First Book of Radio and Electronics." Unfortunately most libraries have pulled his books due to so-called obsolescence. Sad. Oh well.
::
::With wire wound resistors, wattage is determined by wire thickness among other things. Usually the wattage will be stamped upon the resistor. With resistors that are original to the radio, this may not be stamped upon them. After-market resistors--those sold at parts stores like Radio Shack and www.tubesandmore.com--will have the wattage stamped upon them.
::
::With the old glass resistors found in early radios, the wattage capability of these is extremely small. These resistors never were meant to handle currents anyway. They were simply designed in a somewhat compact fashion for regulating control grid bias, which draws very little current, if any. Knowing the wattage of these resistors is unnecessary. Any new resistor of the same resistance (ohms) of any wattage will do.
::
::Regarding carbon resistors, those of old design will usually have a two part color code on them along with a dot as the third color. Some will have the wire leads attached with a molded lead or bakelite end. Others will simply have the wire leads wrapped around a couple of times at the ends and then soldered in place. These resistors had their wattage classified by physical size. Any resistor with a certain width was rated to handle a certain amount of wattage. Various styles of these resistors went by different classification. If you come across these resistors (and you will quite often with 1930s and earlier radios), you will have to consult the various charts availabe for the different types. I have charts for some, but I am not sure if all of these resistors go by the same wattage-size classification.
::
::With more modern carbon resistors, you'll find three or four colored bands for the color coding. The first two are the first two digits of the number. The third color determines the amount of zeros after the number. The fourth, if present, determines the tolerance. I'm sure you already know this color code if you've been working with radio for any length of time. I just wanted to point out this type of resistor. At any rate, the physical size of this resistor determines the wattage, and this classification system has been pretty much universally standardized. Resistors of this type from 50 years ago will go by the same classification standards as brand new resistors. You may obtain charts at the sources I listed above (Radio Shack, library, on line, www.tubesandmore.com, etc.). Here is one such web site that lists color codes and wattages:
::
::http://www.tpub.com/content/firetrucksandequipment/TM-9-254/css/TM-9-254_217.htm
::
::Any resistor that fits a certain size listed in this chart will be of the corresponding wattage. You will never harm a radio by installing a resistor capable of handling more wattage than the original. Wattage handling is simply the ability the resistor has to discipate heat which is generated by the current flowing through the difficult to flow through material. If you install a resistor capable of handling more wattage, it'll run cooler and last longer. Resistors which handle more wattage are generally more expensive, however, which is why radio manufacturers usually use resistors with the lowest possible wattage handling capability.
::
::If, on the other hand, you install resistors that are not capable of handling the wattage that the originals were capable of, you may damage the new resistors. You won't likely damage the radio, though you could start a fire if the resistors heated up enough and burned something else. Also, if they burned up and took a critical load off of the power supply, the excessive voltage within the power supply could burn something else up.
::
::Didn't mean to be too lengthy. Hope that explains everything. There are many types of resistors, so I didn't want to be too general about the whole wattage thing.
::
::Thomas
:
:Steve,
:If you would post your email address (or email it to me) I will send you a .jpg photo that I put together in response to a similar post about resistors some months ago. This photo shows all of the comparative sizes (wattages) of resistors from 1/8 watt up to 25 watts.
:
:Dennis
:Thanks everyone for your great and thoughtful replies. I have posted my email for Dennis to send me the jpeg of his chart. Thanks in advance.
:Steve
:
:
:
:
:::There is no polarity to a resistor. A resistor is simply a device through which current flow is difficult. It does not matter which way the current flows through the resistor. Resistors are usually made up of material that has no polarity preference. Often this material is carbon. Wire wound resistors are the exception. Their wire is nichrome or some other metal that does not conduct current well.
:::
:::Regarding wattage, you can find wattage charts online and at Radio Shack. You may also find them in electrical (radio and electronics) books at your local library. A good book that comes to mind which has such a chart is Alfred Morgan's "Boys' First Book of Radio and Electronics." Unfortunately most libraries have pulled his books due to so-called obsolescence. Sad. Oh well.
:::
:::With wire wound resistors, wattage is determined by wire thickness among other things. Usually the wattage will be stamped upon the resistor. With resistors that are original to the radio, this may not be stamped upon them. After-market resistors--those sold at parts stores like Radio Shack and www.tubesandmore.com--will have the wattage stamped upon them.
:::
:::With the old glass resistors found in early radios, the wattage capability of these is extremely small. These resistors never were meant to handle currents anyway. They were simply designed in a somewhat compact fashion for regulating control grid bias, which draws very little current, if any. Knowing the wattage of these resistors is unnecessary. Any new resistor of the same resistance (ohms) of any wattage will do.
:::
:::Regarding carbon resistors, those of old design will usually have a two part color code on them along with a dot as the third color. Some will have the wire leads attached with a molded lead or bakelite end. Others will simply have the wire leads wrapped around a couple of times at the ends and then soldered in place. These resistors had their wattage classified by physical size. Any resistor with a certain width was rated to handle a certain amount of wattage. Various styles of these resistors went by different classification. If you come across these resistors (and you will quite often with 1930s and earlier radios), you will have to consult the various charts availabe for the different types. I have charts for some, but I am not sure if all of these resistors go by the same wattage-size classification.
:::
:::With more modern carbon resistors, you'll find three or four colored bands for the color coding. The first two are the first two digits of the number. The third color determines the amount of zeros after the number. The fourth, if present, determines the tolerance. I'm sure you already know this color code if you've been working with radio for any length of time. I just wanted to point out this type of resistor. At any rate, the physical size of this resistor determines the wattage, and this classification system has been pretty much universally standardized. Resistors of this type from 50 years ago will go by the same classification standards as brand new resistors. You may obtain charts at the sources I listed above (Radio Shack, library, on line, www.tubesandmore.com, etc.). Here is one such web site that lists color codes and wattages:
:::
:::http://www.tpub.com/content/firetrucksandequipment/TM-9-254/css/TM-9-254_217.htm
:::
:::Any resistor that fits a certain size listed in this chart will be of the corresponding wattage. You will never harm a radio by installing a resistor capable of handling more wattage than the original. Wattage handling is simply the ability the resistor has to discipate heat which is generated by the current flowing through the difficult to flow through material. If you install a resistor capable of handling more wattage, it'll run cooler and last longer. Resistors which handle more wattage are generally more expensive, however, which is why radio manufacturers usually use resistors with the lowest possible wattage handling capability.
:::
:::If, on the other hand, you install resistors that are not capable of handling the wattage that the originals were capable of, you may damage the new resistors. You won't likely damage the radio, though you could start a fire if the resistors heated up enough and burned something else. Also, if they burned up and took a critical load off of the power supply, the excessive voltage within the power supply could burn something else up.
:::
:::Didn't mean to be too lengthy. Hope that explains everything. There are many types of resistors, so I didn't want to be too general about the whole wattage thing.
:::
:::Thomas
::
::Steve,
::If you would post your email address (or email it to me) I will send you a .jpg photo that I put together in response to a similar post about resistors some months ago. This photo shows all of the comparative sizes (wattages) of resistors from 1/8 watt up to 25 watts.
::
::Dennis
From my experience I have seen radios that do and do not follow this practice. In my opinion using a resistor as a fuse is a cheap and unreliable method of fusing a radio. The way I see it, if you want to fuse a radio or some section of the radio, you should use a fuse which is appropriately rated for the situation.
I have seen some manufacturers use resistors rated only to handle normal current flow, and I have seen other manufacturers use the same radio design, but instead use a resistor that could handle more than enough current flow. When you use a resistor that is only rated to handle normal current flow, it often runs kind of hot, which shortens its life (carbon composition). Again, I think that it is better practice to use a fuse if you wish to protect a radio. There is no guarantee that a resistor will completely burn out or burn out enough in time to save valuable parts.
Still, taking into consideration that radio manufacturers sometimes used resistors as fuses, it is possible to cause theoretical damage to a set by replacing resistors with resistors rated for larger wattage. That said, what I said about there being no possibility for harm to be done to a radio when resistors are replaced with larger wattate resistors is wrong. If you replace a power supply resistor with a larger wattage resistor, there is the possibility that you have nullified any protection given by the old resistor. You should only replace resistors with same wattage resistors if you wish to save whatever protection that was originally built into the set.
I don't think that you will in any way void this protection if you installed higher wattage resistors for such things as high resistance plate load resistors, grid leak and bias resistors, A.V.C. resistors, and the like, in the case that you didn't have the right wattages at hand. These circuits don't normally draw enough current to cause harm to a radio, and their associated resistors are often of such high value that a short would not cause a strong enough load on the power supply to be detrimental.
Personally I think that it is poor economy to replace resistors rated for one wattage with resistors rated for a higher wattage, unless the lower wattage is not readily at hand to you and you need a quick fix, or it is apparent that the original wattage resistors were underrated for a particular circuit. When I said that you could replace a resistor with a larger wattage resistor, with no fear of harm being done to the radio, for the most part I was talking about doing this in an emergency, when the appropriate wattage resistor was not at hand. I feel that if you want fuse protection, you should use a fuse.
Thomas
:How is it possible to tell what wattage a resistor is if a schematic is not available? Can you tell by looking at the resistor itself? I have noticed that some of my radios use 1/4 or 1/2 watt resistors. If a radio calls for a 1/4 watt resistor, but a 1/2 watt one is used, will it damage the radio? Also, is there polarity on a resistor? Sorry for the newbie questions.
:Thanks,
:Steve
While I totally agree with Rich's overall assesment of size increase equals wattage increase, that has recently been proven false by replacements I bought for my Tek scope. Some of the precision resistors in it had gone way off value. I hit my buddies at Digikey where I buy most of my replacement caps and resistors. The new 1/2 watt resistors are smaller than the the 1/4 watt ones we are used to.
I really got concerned after my purchase of the last batch. I contacted Digikey who had the resistor manufacturer contact me. They sent me their spec sheets. Included total dissipation as well as de-rating specs (dissipation versus ambient temperature). It was definitely less than half the size of of an identical wattage rating just a few years ago. Asked and they replied that the new materials allowed the resistors to run much hotter but still dissipate the heat without any detrimental effect. Turns out to be a space age ceramic/epoxy constituency that allows that (not wirewound). And in reply to Thomas, they cost less than $.10 a piece. As cheap as any I've ever bought piecemeal. By the by, I replaced with double the original spec'ed wattage.
My suggestion here is that you use the previous supplied size charts to determine what was there but don't be overly concerned by replacing with over-rated resistors. They will either be smaller or, at least, same sized at double the wattage.
Ain't space age technology wonderful.
Rick
:Resistor wattages are related to physical size. The bigger the resistor, the more watts it can handle. Don't worry about using a higher watt resistor to replace a smaller one. That's a conservative choice. The bigger resistor runs cooler and lasts longer. Old radios almost always used resistors of 1/2 watt or higher. 1/4 watt resistors were introduced for transistor and integrated circuit electronics in the 60's and 70's. A 1/2 watt resistor is usually about 3/16" diameter and about 1/2" long. No polarity markings.... doesn't make any difference at all. A one watt might be 1/4" diameter and 3/4" long. Old time resistors from the 20s and 30s were usually larger than modern resistors. They had kind of a "dog-bone" shape. When in doubt, use a resistor of the same value (ohms) and at least as large (physically) as the old or defective resistor. Good luck !
:Rich
:
:
:
::How is it possible to tell what wattage a resistor is if a schematic is not available? Can you tell by looking at the resistor itself? I have noticed that some of my radios use 1/4 or 1/2 watt resistors. If a radio calls for a 1/4 watt resistor, but a 1/2 watt one is used, will it damage the radio? Also, is there polarity on a resistor? Sorry for the newbie questions.
::Thanks,
::Steve
Anyway, I don't care if you put in larger or same wattage. Unless you're a radio manufacturer, a few cents won't matter anyway. I simply stated that replacing with larger wattage resistors is poor economy because if that concerns you, it is. If you don't care, then I don't, either. If you put in a 25 watt 1 meg in place of a 1/4 watt 1 meg, however, that's a bit on the poor economy side. Either way, if it sutes you, go for it. I usually replace 1/4 watt resistors with 1/2 watt resistors unless I have 1/4 watt resistors at hand anyway. The original corresponder to this post was simply asking what the pros and cons of replacing with larger than original wattage resistors were, as well as how to tell the wattage of a resistor. I simply replied. Whether I follow all of the rules myself or not is beside the point. I was simply pointing out what the pros and cons are. Since we all have spelled them out so thoroughly, I suggest that we move on to a new subject and let this rest. It really isn't that big of a deal.
Thomas
Rick
Oh well. Some people make me jealous (like my brother) in how they can write perfectly. Words fall right in line with perfect train of thought.
Thomas
One of my gripes is that the leads on many of today's resistors (and caps, too) are too short. Evidently they are intended to stuff into printed ckt boards rather than point-to-point wiring.
Steven
Agree. Actually the new 1/2 watters are as smaller or smaller than the old 1/4 watters. As to lead length, I mentioned i was working on an old Delmonico in anearlier post. I always re-cap first but this one was especially difficult. Had two can caps, one a 4 section and the other a 3 section. Trying to fit 7 new electrolytics, short leads and all, into the chassis bottom was certainly an excercise in mechanical engineering.
(And a special thanks to Stephen for his kind comments though the real gurus are Thomas, Doug and several other highly experienced rebuilders here on this forum).
Rick
:I've settled on stocking only 1/2- and 1-W resistors, just to keep my inventory down.
:
:One of my gripes is that the leads on many of today's resistors (and caps, too) are too short. Evidently they are intended to stuff into printed ckt boards rather than point-to-point wiring.
Rick
:Doug,
:
:Agree. Actually the new 1/2 watters are as smaller or smaller than the old 1/4 watters. As to lead length, I mentioned i was working on an old Delmonico in anearlier post. I always re-cap first but this one was especially difficult. Had two can caps, one a 4 section and the other a 3 section. Trying to fit 7 new electrolytics, short leads and all, into the chassis bottom was certainly an excercise in mechanical engineering.
:
:(And a special thanks to Stephen for his kind comments though the real gurus are Thomas, Doug and several other highly experienced rebuilders here on this forum).
:
:Rick
:
:
::I've settled on stocking only 1/2- and 1-W resistors, just to keep my inventory down.
::
::One of my gripes is that the leads on many of today's resistors (and caps, too) are too short. Evidently they are intended to stuff into printed ckt boards rather than point-to-point wiring.