bad carbon comp's?

[tacobender]

I picked up a load of CC's and found a large bag of 470R 1/8w gold band, but hardly any of these have measured under 500R, most at around 514R. Does this mean they're on the way out, or is this acceptable? Seems most of the others I've measured came much closer to their design value, but this is the only batch of 1/8thW.

[mcknib]

Carbon comps will be + or - 5% tolerance normally so about 23 ohms some are as much as 20% tolerance or +/- 94 ohms 423 to 517 would be about +/- 10% tolerance although they're not always bang on the tolerance percentage, as you know gold band = 5% (yours) silver = 10% but don't expect measurements to be precise regarding tolerance range. They don't always fall within the specified percentage.

For practical use that amount of ohm's won't matter much for pedal circuits unless they have to be exactly precise or matched in such a case the build doc's would / should let you know.

[PRR]

How do you trust your meter?

[tacobender]

Well I figured there were going to be some variance... ESP with the cc's, but it just seems like these particular ones are far out of range compared to the higher wattage ones I've tested. And I do have to confess my DDM is on the cheap side. I need 470R's in just about everything I want to build so its a little concerning that they may be going bad. And with them being 5% variance I had hoped for better results, considering I've got like hundreds of them. I've been testing them one at a time and soroting all under 500R For use so I guess its just time to plug and pray .. I mean play, LOL. .....anyone else had the same trouble with the 1/8thW?

[plexi12000]

I doubt they are bad...or noisy.  allen-bradley cc's can be way out of tolerance. i know that from experience. 1/4, 1/2, 1, or 2 watt'ers.

but have never had a "noisy" one.  just a note.....i have a meter that cost me around 50 bucks.  and it's off by 20 ohms...so that is a possiblity.

[LightSoundGeometry]

I bought a whole bunch of "mojo" parts one time and they are all over the place. for example, I may use what is supposed to be a 47k for a 68k; or a 160k for a 100K because that is what they are reading out on separate testing devices. one device being a  25 dollar dmm and the other a cheap asian gadget from ebay

I see some of those 1000 dollar boutique pedals with cheap resistors in them on ebay all the time..for hecks sake if you are going to charge a grand or more at least put some old school resistors in there for some eye candy and psychological edge of having magical resistors in circuit 

[amptramp]

Maybe these resistors were in a bag because they were factory rejects.  Maybe they were the next value up, 510 ohms but got into the wrong paint line in manufacture (not likely, though).  Or you are running into an ageing drift process - resistors tend to drift up over the decades due to internal microcracks that develop in the conductive pathways due to thermal cycling and cause current to flow around the crevasses through a longer effective path length.

Not that many circuits require exact resistor values - most require some resistance in the ballpark and a few require matching but it is rare to see an exact value become necessary.

[hymenoptera]

I'm gonna go with your meter is fine and these have simply drifted high over the years. It's usually referred to as "aging up". I've seen 5% carbon comps be as much 20% high before, and it's not that uncommon. Just part of dealing with old components.

Imagine how much "mojo" there is in vintage gear that's simply just from dying parts.. probably more than we care to admit.