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Resistor Identification, How To Tell What Type Of Resistors You have.

SoundOfSound

SoundOfSound

Super Member
When you're looking inside a piece of old equipment how do you know what type of resistors you are looking at. How can you tell the difference between Metal Oxide, Metal Film and Carbon Film resistors. What are the clues to look for? :scratch2:
 
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SoundOfSound said:
When you're looking inside a piece of old equipment how do you know what type of resistors you are looking at. How can you tell the difference between Metal Oxide, Metal Film and Carbon Film resistors. What are the clues to look for? :scratch2:
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These 3 factors are the most telling IMO.

1. Age of the equipment
2. Valves (tubes) or SS ?
3. Experience. (familiarity with the construction techniques of various types of resistor.)
 
What I usually do is take a pic of the item you have in question and then ask here. The only thing you have to be careful of is don't always assume the first answer or any answer is always going to be right. In most cases your going to get good advice from knowledgeable people but sometimes I have found someone to give advice, and believe it or not, they were incorrect so you always need to verify.
 
If you can get a schematic or service manual, that should tell you. Normally a piece of gear will have a default type (carbon comp on old gear, often carbon film in newer gear), and the schematic will just identify which are different types.

Also, smaller resistors are typically carbon comp, carbon film, and/or metal film; larger ones wire wound or metal oxide.
 
Mostly I rely on the age and physical appearance to figure it out. Almost everything I fool with is carbon comp, and those resistors look different than later types. How well they have held value is also a clue. if they're all over the place, usually high, then its almost certainly carbon comp. Those do not age as well as other types.
 
Gadget73 has it right. In the old stuff it is carbon comp' and wirewound in the more recent equipment it is film and wirewound.
 
They certainly do not make it easy to tell. It looks like a lot of the Metal Film resistors are made with a baby blue color and the standard color codes but that is not universal. I did a Google image search and many of them have value codes stamped on them but with all sorts of different body colors.

I was looking at my receiver service manual and noticed that they did not list all of the resistors. The ones that are listed have a CF or MF marking next to them so perhaps they only call out the special parts on the parts list.

The other thing that I noticed was that they denote the Metal Films on the schematic with a ---]VMV[--- type of marking. With brackets pointing outwards from the zig-zag lines on the resistor symbol. I'm not sure if that is an industry wide standard.
 
SoundOfSound said:
They certainly do not make it easy to tell. It looks like a lot of the Metal Film resistors are made with a baby blue color and the standard color codes but that is not universal. I did a Google image search and many of them have value codes stamped on them but with all sorts of different body colors.

I was looking at my receiver service manual and noticed that they did not list all of the resistors. The ones that are listed have a CF or MF marking next to them so perhaps they only call out the special parts on the parts list.

The other thing that I noticed was that they denote the Metal Films on the schematic with a ---]VMV[--- type of marking. With brackets pointing outwards from the zig-zag lines on the resistor symbol. I'm not sure if that is an industry wide standard.
Click to expand...

From my book marks again :D
http://electronicsclub.info/circuitsymbols.htm

Be sure to go to Electronics Clubs home page. This is a great one to book mark. http://electronicsclub.info/index.htm
Check out their downloads.
 
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