Old Resistors

[Josh?]

I recently found some old resistors. My guess, based on the stuff around them, is that they're from the 40s or 50s, but I have no way of knowing for sure.
I've heard lots about old parts sounding special, so is there anything different about old resistors?
Here's a picture for anyone interested:

[GGBB]

There will surely be lots of opinions forthcoming. Those are carbon "comp" resistors, not to be confused with more modern carbon film which is again different than metal film which is probably the most common type used around these parts. Yes - they can sound different because of their different composition. How so depends on the circuit and the ear. The most obvious technical difference is in how much thermal noise they exhibit - carbon comp being the poorest performer of the three.

They also drift in value more over time - measure those ones that you have and compare against their color code values and see how far off they are. This is sometimes claimed to be the reason why vintage circuits sound different than modern day reproductions.

[Mark Hammer]

Have production methods and materials changed over time? Why yes, they have.
Can component properties change with time?    Yes, they can.  But then consider the very idea of NOS.  It presumes that there is a difference between older components that have been used, and those that are in pristine condition.
Is it possible that very old components can change properties over time?  Yes, they can.  Electrolytic capacitors are one very good example.  They can dry out over extended time periods.  Could resistors change over time.  My own sense is "No", but doubtless someone here will have some insider info that contradicts that view.

But the bigger, overarching question is whether there is anything about those resistors that might be predictable.  And there, again, my guess is no.  Those are the very same resistors you'll find in many of the greatest amplifiers from the 50's.  Do the properties of those amplifiers stem from resistors of that age?  Not likely.  WAAAYYY too many other factors to take into account, many of which show clear and strong age-and-use-related change, like speakers, transformers, tubes, and caps.

[thermionix]

Their values can and will drift, even if unused.  I have some NOS 1.5K carbon comps (10%) that read over 3K.  They can absorb humidity over the years and (from what I've read) that can make them noisy.

[Mark Hammer]

I certainly won't and can't contradict that, but I imagine it would depend on how they were stored in the interim, right?

[thermionix]

I certainly won't and can't contradict that, but I imagine it would depend on how they were stored in the interim, right?

I don't know why it happens, that's some PRR territory there.

[Josh?]

I certainly won't and can't contradict that, but I imagine it would depend on how they were stored in the interim, right?

They were stored in a WWII era ammo box with some other non-electrical things. After learning that they are carbon comp resistors, I did some research and found tons of people saying their values drift over time. However, in my case, when I measured the resistances, they were farly close to the values written next to them.

[thermionix]

The picture is too small to see the writing, but how close are the measured values (or written values) to the color band values?

[Josh?]

The picture is too small to see the writing, but how close are the measured values (or written values) to the color band values?

Sorry about the photo .  The values written by them are fairly different from the color band values, but still within the +/- 10% tolerance.

[GGBB]

I certainly won't and can't contradict that, but I imagine it would depend on how they were stored in the interim, right?

They were stored in a WWII era ammo box with some other non-electrical things. After learning that they are carbon comp resistors, I did some research and found tons of people saying their values drift over time. However, in my case, when I measured the resistances, they were farly close to the values written next to them.

According to something I once read, not all brands of carbon comp resistors perform the same in drift. One brand who's name escapes me was known for long term value stability

[Josh?]

So I'm thinking about using these resistors to start building a pedal made out of only special old parts, maybe a tube distortion/overdrive/boost?  However, I only have a few resistors right now.  Where, in you guys' experiences, are the best places to find special old parts?

[PRR]

Allen-Bradly improved significantly around 1960.

These look older.

Will your wings fall off? Your nuclear reactor go haywire?

If you truly believe there is "tone" in old cheap parts, do it. Worst can happen is the amp quits, maybe burns a tube or transformer, probably during an Important Gig.

[amptramp]

Carbon comp resistors have been used for quite a while and they do tend to drift.  The high values (over a megohm) tend to get higher and the low values can go all over the place.  But this is in tube circuits that get hot - you probably are not going to do that.  As for differences in sound, there is supposed to be a varistor effect where the resistance varies with applied voltage but it was never a problem with audio circuits from the era when they were new.

[GGBB]

Allen-Bradly improved significantly around 1960.

That's the brand. Thanks Paul.

[R.G.]

I've heard lots about old parts sounding special, so is there anything different about old resistors?

There are many things different about old resistors, as the posts here show.

Whether they sound "special" or not is problematic. There may have been a grain of truth to this, in odd special cases here and there. In many cases, people may have mistaken an old resistor for what they think of as sound magic. I documented one of the special cases where carbon composition resistors can, under special circumstances, make a difference in sound. It's up at geofex.com; look for "carbon composition resistors".

Sadly, magic DOES exist, but it exists ONLY inside the human brain. What the originators of the "old resistors are magic" thought was incredible sound may not be your idea of good sound. You might think it's awful.

But the hint of magic is an unavoidable lure for hucksters to try to sell unsuspecting newbies a bunch of dumpster rescues as the purest and finest gold nuggets. Hucksters will yell longer and louder than someone simply telling the truth as they know it, as they make a lot of money doing it. So yes, you have read lots about old parts sounding special. Whether you can believe it or not - well, you've proven you're more intelligent than most of the marks by asking first.

Making good sounds relies on much, much more than rubbing old, magic, special parts on a circuit. Congratulations on your caution. Do your own experiments, get and use a DMM to find out that extreme age has done to those old parts, and get prepared to learn. A lot.

[Josh?]

...probably during an Important Gig.

I've definitely had stuff just stop working at terrible times like this.  Good thing is I mostly do jazz so I can just say I'm improvising .

[Jeema]

I replaced a few of these on an old 1940s tube radio not too long ago.  Most of the ones I checked in the radio were slightly high.  A few were very high (one was > 200% out of spec).  I don't think any of them were too low that I recall.

They do have at least one advantage in that they supposedly have better voltage pulse handling than film resistors.  That might be one reason they're still used today in some tube gear (or just the vintage look, I don't know...)

One thing you have to be careful of is when you're soldering them.  Too much heat from soldering can make them drift upwards a few percent or so too.

[R.G.]

I replaced a few of these on an old 1940s tube radio not too long ago.  Most of the ones I checked in the radio were slightly high.  A few were very high (one was > 200% out of spec).  I don't think any of them were too low that I recall.

They do have at least one advantage in that they supposedly have better voltage pulse handling than film resistors.  That might be one reason they're still used today in some tube gear (or just the vintage look, I don't know...)

One thing you have to be careful of is when you're soldering them.  Too much heat from soldering can make them drift upwards a few percent or so too.

Your description is almost exactly what the books say about carbon comp resistors. They drift with age, mostly up, and also with soldering heat. Some drift a LOT.

Carbon comp resistors do have better pulse power handling that most other resistor formulations, and that is why they are still used - along with having a high mythical value for selling to guitar electronicists. When you can sell an item that is old tech - and maybe just OLD - and cheap in quantity to a growing bunch of consumers at extremely high prices, there will be a lot of interest in selling those things. It's like doctors who specialize in diseases of the very wealthy. The pulse handling ability isn't particularly useful in guitar amps, where there isn't much in the way of pulsed power.

Carbon comps are also more mechanically fragile - I've seen them cracked in the middle of the tube, or with the lead and end cap separated from the body. And CC has more noise than other resistors of similar value and power rating.

What CCs had going for them was that they were cheap, back in the day. Today, with the myth of magic sound qualities and scarcity, and a new generation who only knows the myth, not the real info, they can sell for dollars each, not the pennies they would if industry still thought they were worth the effort.

Oops - my opinion is showing.   

[GGBB]

Carbon comps are also more mechanically fragile - I've seen them cracked in the middle of the tube, or with the lead and end cap separated from the body.

Thanks RG. Something I remember being taught a quarter century ago now makes sense. We we're to never bend the resistor leads too close to the body. I could never recall the why, if ever we were told.