Carbon Comp Resistors discussion??

[Jalmeida]

What’s everyone’s take on Carbon Comp resistors? Mojo and cool factor? Or real tone difference? Worth the added expense/inconvenience in sourcing?

I have been using Carbon Film as I am
not a mojo guy. But some builders I really look up to that know their stuff use them. So it has had me re-thinking. And it seems answers are all over the place. If I were building to sell amps, carbon comps seem like a no-brainer. People love paying for that. What does EL34 land think?

[Dave]

I'm not a big believer in voodoo. I used them to replace bad carbon comps in vintage amps in an effort to keep things as original as possible. On my own stuff, I use whatever I have available with some exceptions. Carbon comps can be a little problematic as plate resistors, so I try not to use them there.


Yes, I have read that carbon comps have special voodoo and that the voodoo is measurable on special ghost busters equipment. Whatever... any ability that I might once have had to distinguish that level of audio cork sniffing was wiped out by loud amps and jet engines.


Dave

[sluckey]

I have a collection of 1/2W, 1W, and 2W NOS mil spec CCs. All 5% tolerance. Practically every value made. If you figure each resistor costs 10 cents, I must have a couple hundred dollars worth. Every one has drifted up and out of spec. That's why I quit using CCs.

[Jalmeida]

any ability that I might once have had to distinguish that level of audio cork sniffing was wiped out by loud amps and jet engines.
Dave

Same here. I work in Avionics on aircraft. Between that, years in the Airforce and music my ears are doomed.

[Jalmeida]

I have a collection of 1/2W, 1W, and 2W NOS mil spec CCs. All 5% tolerance. Practically every value made. If you figure each resistor costs 10 cents, I must have a couple hundred dollars worth. Every one has drifted up and out of spec. That's why I quit using CCs.

Yeah, I have heard but not confirmed that NOS caps do the same thing. And I also know that many of the “cork-sniffers” amongst the enthusiasts world swear that those drifts in values are what makes old amps sound so much better. Which I buy that to a certain degree. Although i’d need a blind listening test before I would believe these people. I know that Lyle Caldwell mods some newer Vox AC30 amps with drifted value capacitors to duplicate that magic/mojo.

[bmccowan]

I use metal film for all the 1/2 watt applications. For critical spots I use the Vishay/Dale CMF 60s. Make a difference? I use some 1 watt carbon film. The only time I use older carbon comp is if repairing a true point to point amp and want the stoutness of those thicker leads. I turn 70 in a few weeks - the Mojo is about used up.

[bmccowan]

I have a collection of 1/2W, 1W, and 2W NOS mil spec CCs. All 5% tolerance. Practically every value made. If you figure each resistor costs 10 cents, I must have a couple hundred dollars worth. Every one has drifted up and out of spec. That's why I quit using CCs.

Hey Steve - you could scrap off the 5% band, paint on a 10% band and be back in business.

[Dave]

"Yeah, I have heard but not confirmed that NOS caps do the same thing. And I also know that many of the “cork-sniffers” amongst the enthusiasts world swear that those drifts in values are what makes old amps sound so much better. Which I buy that to a certain degree. Although i’d need a blind listening test before I would believe these people. I know that Lyle Caldwell mods some newer Vox AC30 amps with drifted value capacitors to duplicate that magic/mojo."



The caps thing brings up a hole other conversation... I hate it when guys get a vintage amp (Blackface or something like that and then go through it and shotgun every capacitor in it). Yes, those old caps drift upward, but if they don't leak, leave them alone. I once built an entire amp using nothing but old used black beauties just to prove that point. In fact, I did my best not to use any new parts, except electrolytics, anywhere in the amp. It's an outstanding-sounding amp and it was super cheap to build.


Dave

[bmccowan]

The caps thing brings up a hole other conversation... I hate it when guys get a vintage amp (Blackface or something like that and then go through it and shotgun every capacitor in it). Yes, those old caps drift upward, but if they don't leak, leave them alone. I once built an entire amp using nothing but old used black beauties just to prove that point. In fact, I did my best not to use any new parts, except electrolytics, anywhere in the amp. It's an outstanding-sounding amp and it was super cheap to build.

In most cases I agree - but I recently rewired 4 DanElectro made Silvertones and Airlines that all had purple/greenish Sangamo caps. For all 4 amps, those caps had drifted 50%+ and over 1/2 of them leaked DC. I replaced them all, because things would only have gotten worse. Some caps, like the blue molded Mallory caps in BF Fenders are robust - some are not.

[sluckey]

I have a collection of 1/2W, 1W, and 2W NOS mil spec CCs. All 5% tolerance. Practically every value made. If you figure each resistor costs 10 cents, I must have a couple hundred dollars worth. Every one has drifted up and out of spec. That's why I quit using CCs.

Hey Steve - you could scrap off the 5% band, paint on a 10% band and be back in business.

Better yet, maybe I could sell them to someone that has experience painting resistors. Know anyone?   

[bmccowan]

Oh - you know him better than I do.

[Jalmeida]

"Yeah, I have heard but not confirmed that NOS caps do the same thing. And I also know that many of the “cork-sniffers” amongst the enthusiasts world swear that those drifts in values are what makes old amps sound so much better. Which I buy that to a certain degree. Although i’d need a blind listening test before I would believe these people. I know that Lyle Caldwell mods some newer Vox AC30 amps with drifted value capacitors to duplicate that magic/mojo."



The caps thing brings up a hole other conversation... I hate it when guys get a vintage amp (Blackface or something like that and then go through it and shotgun every capacitor in it). Yes, those old caps drift upward, but if they don't leak, leave them alone. I once built an entire amp using nothing but old used black beauties just to prove that point. In fact, I did my best not to use any new parts, except electrolytics, anywhere in the amp. It's an outstanding-sounding amp and it was super cheap to build.


Dave

I agree. I see vintage Vox ACxx amps with the vintage tone and coupling caps changed to modern orange drops and just shake my head. Like the term recap was taken litterally with no consideration for condition. Just blanket changed. A shame.

[acheld]

I'm with bmccowan on the resistors.   I got tired of keeping different spec resistors, so now I preferentially use 1 watt Vishay Dale CMF series.

I confess that the brown color is unappealing, so I may do a Yeatzee and paint all the buggers purple and red!  Or maybe orange, so I can have "orange drop" resistors.  Now there's a thing.

[Jalmeida]

I'm with bmccowan on the resistors.   I got tired of keeping different spec resistors, so now I preferentially use 1 watt Vishay Dale CMF series.

I confess that the brown color is unappealing, so I may do a Yeatzee and paint all the buggers purple and red!  Or maybe orange, so I can have "orange drop" resistors.  Now there's a thing.

Not to mention it is really convenient to buy large assortments of carbon comps in lots of values. Instead of buying onesee twosee Carbon Comps. If I could find a thorough assortment of carbon comps i’d be more inclined to use them regularly. But they are also overpriced from what I have found.

[passaloutre]

Edit: never mind, somebody made the same joke

[PRR]

One of my early jobs was an Arkay hi-fi (not even 15 years old at the time) that motorboated. My dad suggested driver unbalance. Sho nuff, of two 100K 5% parts, one was 110k and the other was over 150k and rising.

In a world of Ford Flatheads, which needed a valve-job every few years, drifty resistors were acceptable because they were CHEAP. They were not as bad as inked-paper resistors.

Of course after Maytags which ran 40 years without a burp, we get washing machines with switch-mode motors which seem destined to die in 7 years. (Ours ran 14 years but only two people here.) So maybe short-lived CC is back in style?

[Joel]

Here's a trick I learned from old US Air Force tech manuals when I was posted to a RAAF F-18 Avionics workshop.  If you really want (or need) to use those out of spec CC resistors, it's really easy to bring them back into tolerance (and bring that mojo back).  Dry them out by baking them at 90 degrees C (194 degrees F) for 24 to 48 hours.  Once they cool back down you'll find that most will be back in tolerance.  The primary cause of CC values drifting is moisture absorption and baking just dries them out.  To keep them within tolerance you'll need to coat them with an impermeable coating.  A good epoxy would do the trick.  Coat them as soon as you can handle them.  I found that they can drift again quite quickly in high humidity environments.

[pdf64]

PCBs for kit that’s going to be in harsh environments are given a dip or spray with conformal coating, to prevent condensation / ice frost wreaking havoc.
So that type of stuff might work for freshly baked CC resistors?
https://uk.farnell.com/mg-chemicals/4223f-55ml/coating-conformal-55ml-bottle/dp/3255891

[EL34]

What does EL34 land think?

I used 1% tolerance metal films on all my amp builds starting in 1993

[HotBluePlates]

... I have read that carbon comps have special voodoo and that the voodoo is measurable on special ghost busters equipment.  ...

It's a real thing, but only adds a small amount of distortion to some carbon comp resistors, in some circuit positions.

It's called "voltage coefficient of resistance" and is shown on some carbon comp data sheets (when they're being complete).  Basically, when there's a lot of voltage across the resistor, it changes its resistance.  So AC voltage that swings through zero has little-resistance-change near 0v but larger-resistance-change during a 100-200v peak.  And even this "larger" change might not be enough ohms to make an audible difference.

This is why some will say they want carbon comp resistors for plate-loads (where voltage swing is larger) or late in the amplifier (like phase inverter load resistors, or grid bias/reference resistors of output tubes).  However, having larger voltage drop across a resistor will make it noisier in some cases (some older noise-tests applied 100-150v DC across a part, then detected/amplified any AC noise present).


Myself, I mostly just use metal film resistors unless I'm repairing a vintage amp.  The metal films would probably be just fine, but the vintage amp thing is trying to replace like-for-like.

Capacitors in vintage amps are a different thing; wildly different outcomes depending on the specific parts being discussed (and the tech they used in their construction).

[Joel]

PCBs for kit that’s going to be in harsh environments are given a dip or spray with conformal coating, to prevent condensation / ice frost wreaking havoc.
So that type of stuff might work for freshly baked CC resistors?
https://uk.farnell.com/mg-chemicals/4223f-55ml/coating-conformal-55ml-bottle/dp/3255891

I can't remember the types of conformal coatings we typically used.  Too many years... too many beers.  I think the main one was a urethane type.  For our purposes though epoxy might be the cheapest and most readily available.

[PRR]

Clear nail-polish, supermarket or drugstore.

[Electron Tornado]

Clear nail-polish, supermarket or drugstore.

A fellow I used to know who was an electronics repair tech suggested the same thing. He said it also worked on copper traces on PCBs or vero to keep the copper from corroding.

[Jalmeida]

I know in my electronics school they taught to use spray urethane similar to this made by CRC for circuitsboards and components.

https://www.crcindustries.com/seal-coat-174-clear-urethane-coating-11-wt-oz/

[dpm309]

I built a '59 Bassman clone (5F6A) using CCs several years ago. Was very noisy so I replaced every one with 1% metal film and the amp is now quiet. Did not affect the tone one bit. I have used metal films on all of my builds since.

[Jalmeida]

So looking into the voltage coefficient I found a few different numbers mentioned as a comparative numbers between carbon film and carbon comps. But they were fractions of a percent different. I believe their is more to be found on these numbers I haven’t found. I just haven’t find a clear number that give relevant figures. And I am sure inductance differences come into play between one versus another too. 🤷🏻‍♂️

I guess my question is, can it be identified in a blind listening? Say two different Princetons one with CCs and the other of Carbon or metal
Film types. And besides noise would there be any tonal differences that can be differentiated? 

[66Strat]

It comes down to personal preference. There may be a slight difference in tone. But, in my opinion the difference is more than offset by the increased noise floor (HISSSSSSSS). The only place that I would use them would be in restorations projects of vintage amps.

However, if you want to try carbon comps, the attached article by R. G. Keen offers some suggestions on how to best implement them.

http://geofex.com/article_folders/carbon_comp/carboncomp.htm

[bmccowan]

I really like the R.G. Keen piece and had forgotten about it. Its a big part of the reason that I stopped using CC resistors years ago. I am not concerned about trying to keep an amp looking original on the inside. If I can get an old amp to work right and sound right, I am happy.

[Jalmeida]

It comes down to personal preference. There may be a slight difference in tone. But, in my opinion the difference is more than offset by the increased noise floor (HISSSSSSSS). The only place that I would use them would be in restorations projects of vintage amps.

However, if you want to try carbon comps, the attached article by R. G. Keen offers some suggestions on how to best implement them.

http://geofex.com/article_folders/carbon_comp/carboncomp.htm

A really great read. Thanks for sharing.

My AC30/4 build I am in the middle of I used as many CCs as I could. Mainly to see what all the hype is about for myself. Not sure my ears are tuned well enough to tell. But we shall see..

[passaloutre]

Has anyone used the PR02 resistors from Vishay?

https://www.tubesandmore.com/products/resistor-pr02-vishay-bc-2-watt-power-metal-film

They're metal film, rated for 2 watts, but they have a "vintage" look (reddish brown), and a very small size for their rating (slightly larger than most 0.5W resistors), which may make them suitable for carbon comp replacement.

[acheld]

Has anyone used the PR02 resistors from Vishay?

Yup.  They work fine of course.   And it's true that their appearance is "closer" to vintage than what I normally use (Vishay CMF).

[66Strat]

I really like the R.G. Keen piece and had forgotten about it. Its a big part of the reason that I stopped using CC resistors years ago. I am not concerned about trying to keep an amp looking original on the inside. If I can get an old amp to work right and sound right, I am happy.

There is a ton of information on R.G.'s Geofex site. I use it primarily for info on Vox solid state amps. I had a Vox Beatle amp when I was a teen. It had more than its share of problems, but sounded great when cranked enough to engage the limiter. With nostalgia beckoning me, I've been playing with the idea of building a SS amp loosely based on the Vox SS AC30 using current production low noise JFET ICs. My idea is to incorporate the limiter circuit of the Beatle amp in a master volume arrangement.

[Yeatzee]

I have a collection of 1/2W, 1W, and 2W NOS mil spec CCs. All 5% tolerance. Practically every value made. If you figure each resistor costs 10 cents, I must have a couple hundred dollars worth. Every one has drifted up and out of spec. That's why I quit using CCs.

Hey Steve - you could scrap off the 5% band, paint on a 10% band and be back in business.

Better yet, maybe I could sell them to someone that has experience painting resistors. Know anyone?   

Sounds like a cottage industry just waiting to be started. I'll get right on it!

 

[sluckey]

Sounds like a cottage industry just waiting to be started. I'll get right on it!

 

I was wondering where you were. What's your next project. Pro Reverb? Should be a piece of cake since you just finished the Vibrolux. Probably reinforce some of the stuff you just learned too. Platefire has a current thread on a Pro Reverb. His was a real mess when he got it. He brought it to life years ago but can't seem to keep his hands out of it.   

[Yeatzee]

Sounds like a cottage industry just waiting to be started. I'll get right on it!

 

I was wondering where you were. What's your next project. Pro Reverb? Should be a piece of cake since you just finished the Vibrolux. Probably reinforce some of the stuff you just learned too. Platefire has a current thread on a Pro Reverb. His was a real mess when he got it. He brought it to life years ago but can't seem to keep his hands out of it.   

Pro Reverb is getting a 3 prong this week for sure (already shocked me), and then evaluate the inside. It actually sounds great, doesn't seem to have any hum or anything that would suggest there are major issues. Trem doesn't work so that's on the list as well.

But I'm actually eyeballing my other amps for the next major project. I've got a 1964 Vox AC10 I'd love to make sure is good to go, but I've been waiting as it's more intimidating than the Fender stuff.

[HotBluePlates]

... Trem doesn't work so that's on the list as well. ...

Every Fender amp larger than the Princeton Reverb must have the footswitch plugged in to activate the tremolo.  Many new buyers wrongly inter[ret this behavior as "broken trem" when it's perfectly normal.

It has to do with Fender's method of "shock-starting" the trem oscillator when switched on.  Oscillators in amps that didn't have such a circuit (like some Ampeg amps) can take a couple seconds to get going when switched on with the footswitch.

[Yeatzee]

... Trem doesn't work so that's on the list as well. ...

Every Fender amp larger than the Princeton Reverb must have the footswitch plugged in to activate the tremolo.  Many new buyers wrongly inter[ret this behavior as "broken trem" when it's perfectly normal.

It has to do with Fender's method of "shock-starting" the trem oscillator when switched on.  Oscillators in amps that didn't have such a circuit (like some Ampeg amps) can take a couple seconds to get going when switched on with the footswitch.

Yeah I've got the footswitch as well as a shorted RCA plug to get around that, still nothing. Assuming the little roach or whatever it's called is bad but I haven't opened it up yet to see if there's blinking