Any use for 1/2W Carbon Composition Resistors

Discussion in 'General Electronics Chat' started by Stuntman, Aug 4, 2011.

  1. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    I've come across a nearly full E24 set of 1/2W Carbon comp resistors. I understand these have some shortcomings in terms of long term stability, so I'm debating whether to keep them around. I also have a fair number of CC power resistors.

    I really can't think of many applications for my personal use, is there any use for these any more? Any kind of market for them? (like for nostalgic electronics repair)?

    Don't want to add to the black hole of stuff I keep that I'll never use.

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It would be interesting to sample them and report back on what your findings were.

    I had some 1% mil-spec carbon comp. resistors that were hermetically sealed in foil & plastic pouches in 1968 that were left over from a project I did in the 70's that I opened up and tested a few years ago. I was somewhat surprised at how far they had shifted; the resistance was always more than the resistors were marked; from roughly 5% over to in excess of 200% of what they were supposed to be - even though they had been unused/sealed for 40 years.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Might be worth tossing up on EBay and see if anyone bites. Otherwise CC resistors are just horrible things and their passing is not to be mourned.

    My last place had some DOD contracts where we were firmly directed "no substitutions," including the now obsolete CC resistors. There are houses out there that collect obsolete stuff to resell and we had to buy from them. Values had drifted way out of tolerance to the point the sellers would not accept returns for any reason, even if that reason is the 1.0K 10% resistor was reading 2.0K.

    So there is still a small but dwindling market. Maybe someone who thinks the colors are pretty will buy them to make bracelets like an ex of mine did.
     
  4. iONic

    AAC Fanatic!

    Nov 16, 2007
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    Well,
    I didn't know this at all. ...and it's a good thing to know if you hope your project is going to perform for many years to come. Maybe this thread will be the straw that broke the camel's back!
     
  5. Stuntman

    Thread Starter Active Member

    Mar 28, 2011
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    It would be interesting to see on average how far off they are at this point. They were not stored in optimal conditions. I've played with a few of the 1/4W, they had drifted about 10% high.

    Although that may not seem bad, I have a real concern as I've heard they absorb moisture, and upon soldering, can have a large permanent shift in resistance. Sounds like a recipe for many headaches over some cheap resistors.

    I may see what I can find, I'd hate to throw them all out by principle.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    Just to make sure people know what we're talking about, the carbon composition resistors we're referring to have a cylindrical body, and are frequently a dark brown in overall color; like this:

    [​IMG]

    [​IMG]

    [​IMG]

    Carbon film resistors are not prone to changing resistance; it's easy to tell the difference by the "dumbbell" shape:

    [​IMG]

    I had some carbon film resistors I'd bought 20 years ago; they are still measuring within tolerance.

    The one thing that carbon film resistors are really good for, is that the high-value resistors are very frequently used as forms for winding inductors. When used as such, any change in resistance would be of very little significance.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    Carbon composition make good inductors. I saw the drift Wookie is talking about, even when new the act of soldering would shift them substantially.

    Something Forrest M. Mims III made a point that many circuits don't need precision though, a lot of electronics is surprisingly immune to tolerances. You have to judge the application, because a lot of times it ain't so.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    I found about 1000 of these locked away in an old cabinet at work. Judging by their appearance and the age of the other things in the cabinet I think they are from the late 70's/early 80's. So far every one of them I have measured has been within tolerance.
    [​IMG]
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Our company has used the CC resistors for years in their attenuators for RF.
    They where mounted with a couple in parallel for more power, as they where used for transmitters capable of RF pulses of 1 kW.

    Bertus
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    I tend to stock 1KΩ more than most resistors. If it isn't critical then around 1KΩ is a good value, not too high current but substantial enough for most LEDs and transistors.

    If you use the resistors for inductor cores you want higher resistance values, starting 10KΩ, preferably more.
     
  11. RRITESH KAKKAR

    Senior Member

    Jun 29, 2010
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    @ Our company has used the CC resistors for years in their attenuators for RF.

    Which company, name please.....
     
  12. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I am working for Bruker for almost 25 years.
    The company is specialized in analytic measuring equipment.

    Bertus
     
  13. #12

    Expert

    Nov 30, 2010
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    Fourty years ago, many easy repairs on vacuum tube TV's happened because any CC resistor over 1 meg would be a good suspect. One TV had a 10 meg in the RF AGC line. You could almost fix this one over the phone.

    Now, carbon film resistors are not suspect. I have some 1% carbon films from 1973 and all of them are still in spec.
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    The repairs I loved (not) were the hairline cracks. The wires would keep the resistors in place, looking normal. If you were really lucky it would make intermittent contact.

    Come to think of it I don't think I've seen that from carbon films.
     
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