Carbon comp resistors

[tsutt]

Are they different from carbon film resistors? noise wise or other.

[Ron Worley]

CC are generally noisier and drift with age and temp. CF are more stable, but purists swear by CC as more vintage authentic. There are all sorts of opinions and voodoo lore out there.

[pops]

According to David Funk CC should be used in a few key places, the rest it makes no difference, I like metal film if i am not using carbon comp.

[R.G.]

There is a long dissertation on the mojo of carbon comp resistors at http://www.geofex.com .

Carbon comp *was* cheaper to make than other forms of resistors back in the 40s, 50s, and 60s. Improved manufacturing made carbon film cheaper and tighter tolerance after about the 1980s. Metal film is becoming about as cheap as carbon film these days.

Carbon comp has a higher pulse energy tolerance than most other forms of resistor.

In today's market, carbon comp is no longer cheaper, as the manufacturing base to make them cheaply is long destroyed. They are still wider tolerance, by nature. They are noisier.

Carbon comp does have a soft form of distortion that is liked by musicians, but it happens ONLY with signals bigger than about 70V peak to peak.

So they're more expensive, wider tolerance, and noisier. They offer an advantage in sound in only one or two positions in a tube amp, and NO positions in low voltage pedals.

[Leo_Gnardo]

One place you do want CC's is grid stops, those 1k5 or 5k6 on output tubes (or another value that suits you), same 68K commonly found in Fender & Marshall inputs. Here again you may vary value as your ear guides you.

CC resistors tend to be more linear in the RF region, tend not to act as inductors the way spiral cut MF, MOX, CF resistors are. Before everything went surface mount I noticed all the R's in quality brand guitar wireless transmitters (Nady for instance) were 100% CC.

In applying grid stops we're trying to limit RF access to control grids. It makes sense to have an R that doesn't become more of an impedance as you go up in frequency.

For those who don't mind screen grid R's acting as fuses, the old 1W 470R works just fine.

CC's in power supplies, not so much necessary anymore. MOX works just fine for that, WW also. For those that like carbon, Mouser still carries 3W IRC but not many values and they may cut the line out. Last time I ordered by phone the order taker said they "weren't a popular item." They do have 'em in useful 470R & 100K values. Don't grab 'em all guys, leave some for me, OK?

OT but here goes anyway: Something a bit worrisome is the physical shrinkage of modern resistors. A 2W part looks like a quarter-watt used to. Despite claims they can "take the heat" we've seen some cases where they can't. For instance, smart techs will go the extra bucks and time to track down 3 watt wirewound 1% 1 ohm resistors to install as cathode current sensors in output tube circuits. Those who have tried the modern 1W mini resistor find it acts as a dandy mini fuse in this application, can't take the momentary burst of heat at switch-on I s'pose.

Of course any or all of the above may be persistent web legends & fantasy, or the summation of continuous hallucinations of generations of ham radio geeks and other electronic thrill seekers.

[tsutt]

Thanks for the info.

[Meat&Beer]

This website gets tossed around here a lot, maybe you have/haven't already seen this regarding resistor types:

http://www.aikenamps.com/index.php/resi ... -it-matter

[tsutt]

very interesting

[Milkmansound]

I have a huge stash of vintage Allen Bradley carbon comps, and I use them for nearly 100% of my amp circuits. The one spot I prefer carbon film is in the reverb mix circuit because the CC can get a bit noisy there.

Any noise they add can be engineered out by balancing the gain structure of the amp in a different way. My amps are very quiescent, but if you turn em up to 10 yeah, you will hear some hiss from those resistors... but then compare that to the output from the guitar and its a non issue.

I have tried carbon film in other places, and the same amp is not quite the same with them in there. Not sure why - some things don't make sense based on numbers. I get a lot of criticism about it from Facebook tube hobbyist types - same as you would if heaven forbid you ground under a transformer lug (which I do not do, but its perfectly fine if you do it because there are no rules in this game)

The new production CC resistors sold by CE Dist or AES sound great too. I say go for it, don't worry about drifting and noise. Its all mojo baby!

[R.G.]

I get a lot of criticism about it from Facebook tube hobbyist types - same as you would if heaven forbid you ground under a transformer lug (which I do not do, but its perfectly fine if you do it because there are no rules in this game)

Well, in this case there are rules.

If you mean attaching AC safety ground under a transformer lug, UL standards and IEC international standards do not allow it, and any inspector will not sign off on it for safety reasons. This practice used to be allowed, but no longer is, so they all check for it.

In the USA you are not required to get UL approval, but not getting it leave you at risk for bigger damages if there is a court case over shock or fire with the amp. As I understand it, it used to be that to sell in Europe, you had to be approved by one of the national testing labs, and after you did that, you were immune from damages based on electrical safety. No longer. Today, the EU allows people to sue for damages even if you had it inspected, much like the USA model. And if the inspection labs ever test an amp and find that it does not have a valid CE mark ( that is, both has the mark and passes the standard when tested ) then they can forbid all further sales in the EU, and maybe other penalties.

If you meant grounding signal ground to the chassis under a transformer lug, sure, that's fine. It's just sometimes more reliable to ground it somewhere else unless you're doing fancy footwork with star washers to bite into the chassis and solder lug. That was in fact why the safety guys forbade using it for safety ground.

[Milkmansound]

oh yeah - I meant grounding cathodes of the power tubes or something like that. For some reason people go crazy about the path to ground for the audio circuit. No rules there.

Safety ground is a whole other thing