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carbon composition - 2 types

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Allen Bradley composition resistors seem to be the favorite. As you probably know, they have the solid slug element. In the 60s and 70s there were probably 20 different companies that made the slug type. Today there are about 7 companies making them.

There was, and still is, another type of composition resistor. It was made by TRW/IRC and is still available through IRC, but it is made for IRC by Kayama-Japan and there is no stocking distributor to be found.

This TRW/IRC (the TRW aspect of the name has since been dropped) resistor has a glass tube inside with a thick composition film on it. It is not spiraled and is purported by TRW to have better high frequency characteristic. As far as I can tell (TRW did not answer my email) it has the same surge capability as the slug type. It is not carbon film, it is composition film and drifts with age as the Allen Bradley type does.

I am looking for opinions on carbon composition.

(1) Is the Allen Bradley better than other slug types?

(2) Is the TRW type with the glass tube undesirable in any way?

It seems to be the consensus among technical folks that the reason the carbon comp resistor is unique is that the voltage coefficient of resistance is very high. That is, the resistance goes down when the voltage across it gets high resulting in a unique type of distortion. When used as plate resistors they distort the amplitude of the waveform.

The TRW type has the same voltage coefficient as the AB type.
 
You have found yet another supplier. These appear to be the slug type.



I wasn't sure if this forum or musical instruments would be the right one.



Perhaps I didn't make the question clear.


I am trying to found out if carbon comp users do not like the TRW film on glass tube type. Also, is there a preferred composition resistor in general?
 
hailteflon said:

I wasn't sure if this forum or musical instruments would be the right one.

I am trying to found out if carbon comp users do not like the TRW film on glass tube type. Also, is there a preferred composition resistor in general?


I'm using metal oxide and metal film for both HiFi and MI.
Although in the past I've used carbon types in front end stages, the typical cracked carbon hi stab 2-5%% types aren't around anymore so I've had to resort to modern metal types to keep pentode 1st stage noise down. Despite the voltage v.s resistance not being linear with carbons I've not had any undesirable musical effects using on metal film types, metal on glass etc. I choose mainly the working voltage parameter.
I strongly dispute claims by those in the HiFi ratpack that can really tell differences. If there are subtle differences then as the audio frequency is so low compared to RF then something else in the circuit i.e amp circuit & output transformer quality is not up to par or using old tubes. Tube amp layouts are often so birds' nested that any extra inductance created by wiring far out-swamps any internal component inductance, and worse still loudspeaker manufacturers often use wirewound typs for crossover networks. So be it !
Sorry if I've taken my gloves off ?

richj
 
Stuff from the junk box. Top LHS older vintage wax impregnated rod power carbons. Nom cold value as stated. Hot value +50% not unusual..
Top RHS rare wax impregnated <high stab cracked reworked carbon> with pink and other stability ind bands.These held values within stated % cold and hot. Hard to find.

Lower RHS bog standard carbon res. Some 20% values measure 50% Ohmage increase. Drift with time. Most vintage carbons can survive massive B+ surges whereas m/o types can change.

Lower LHS modern 1% 2% m/o film and glass TRW lowest. Stable cold and hot.

The most signifigant change is wattage v.s downsizing. The metal film power grey (lower left) can accept same power with hardly any coefficient change compared to wild temp drift of the top left rod types.
Considering most of the carbon types were fitted during the 1940-60‘s TV and audio sets, the sound quality of some vintage tube amps with these resistors fitted is still just as good as the modern stuff. Proof that tight tolerance is never required for tube work.

Carboot sales in the UK often come up with such goodies.

richj
 

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high stab cracked reworked carbon

When you say "cracked" do mean that the resistor was cracked and they repaired it? possibly with wax?

The lowest on the LHS may be a TRW metal film, but it is not a carbon composition. TRW cc are molded dark brown. I don't think there is any glass in the TRW.

The fourth from the top on the RHS is a RCR20 (M39008) military carbon comp. That is about as good as they get. They are out of production worldwide. NASA published a bulletin about how they have no supplier. I found the NASA document on the web while googling carbon comp.

The three at the top on the RHS are what you are calling wax impregnated? They are so dirty they would have to have wax on them.

I recognize those, from sometime somewhere. Are those of British origin? The pink band is strange. Have you broken one open to see if they are carbon? Some of that type are wire as I recall.
 
Radiotron hb/4th ed doesn't digress deeper than we are here.
The pink salmon end colour types are high stab, the cracked carbon is a solid composition but the carbon has been structually altered, (akin to annealing steel etc at the upper critical temperature structure is finer grained then processed.)
Farnell also stocks a carbon ceramic but that is spiralled with restricted values i.e stock no's 1219226.

I squeezed the larger 47K, this is cat cracked carbon BS.1852 1952 stock and despite faulty end caps the carbon is finer in one rod. I can bust some other open but need more time to set up EOS etc.

This may seem the perfect specimen which one is after, soon after carbons were no longer manufactured, the world went into helix/spiral construction.
I will look for a typical specimen out of the junk box.

richj
 

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Here is another variant...a 22K 2W with eroded surface with spiral cut clearly visible. This was typ manu of early 1970's. On the package had limited working volts to 350V. I am probably correct that this is the type that everyone seems to loathe.

richj
 

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Thanks for the pics. I will try to find the Radiotron h/b free download.

Are the resistors in the pics soft? They look like cement.

What are the colors on the 4th resistor from the top on the RHS? Is that org-blk-blk-gold-blue? If so, what is the blue 5th band?

I have tried to access UK defense documents, but they don't allow public access without permission.

The US military uses a 5th band for military reliability, but they are either yellow, orange, red, or brown. (red and brown are rare). I did find evidence that the UKMOD (Min of Defense) has their own spec sheet DEF5112A, but it is not to be found on the web. at least not for free. US military info does sometimes say that a resistor is DEF5112. The UKMOD lets you see their doc index for free. The resistor specs are now DEF-STAN-59-30. USA specs are also confusing, but they are available for free download. It must be all that British Secret Service business, for 00s only.

I'm going to do some more searching for British specifications such as BS1852 (British Specification 1852?).

Allied carries a full line of traditional carbon comp and also the ceramic carbon type OX/OY. The ceramic carbons do not appear to be spiraled.

Evidently "cracked" means ground to a fine powder. This is interesting because the USA military/industrial spiraled carbons have better stability and noise than usual commercial grade. I have never found much info on the actual chemistry of the film.

I'll get back later and look at your pics. Post a close-up of the one with the blue 5th band.

After a closer look at your first pic, there are five of the old type that you are opening up, and only one has a silver or gold tolerance band. These are strange. Are the black and pink 4th bands the tolerance? Is that a brown 4th band and a pink 5th band on the large one at the top?
 
"Cracked" in this context refers to a process of depositing a carbon film on a ceramic rod out of a very hot hydro-carbon vapour. A spiral is then cut in the film to form the resistor. The "cracking" means separating out, in this context, and is not to do with grinding carbon into a powder. There is a clear explanation in Dummer's book, "Fixed resistors" (Pitman 1956).
 
depositing a carbon film on a ceramic rod out of a very hot hydro-carbon vapour. A spiral is then cut

This sounds like common carbon-film technology.

Vacuum sputtering is the name?

Metal-films are made much the same way, but with different film.

I have tried to find the actual difference between the carbon-comp and carbon-film mixtures. All I could ever find on the web was that
(1) carbon comp has a specific requirement that it have some sort of binder in it, and nothing else besides carbon.

(2) carbon film can be anything.

Evidently the cracked carbon technology was the name for the more stable film that replaced carbon composition. Carbon-comp can be either a slug type or a film on a tube. I found a link last night from a google-book that showed the film on glass type of CC and they called it "carbon-film". The spiraled resistor (that is commonly called "carbon-film") is called cracked-film in this book. The book is titled Electrical Craft Principles. I can't do a copy-past on it, it won't work. Pyrolytic resistors is another name given for cracked carbon.
 
I've enclosed a close up of the resistor in question. None are spiral but encased in a ceramic sheath. There were xmillions made of phenol bakelite ones too.
The lower one in the photo someone pointed out was US MiL = correct. that reads 10R
The large 47K is a 1953 Standard Telephone Cables UK, High stab (pink band) brown is 1% tolerance. (which it is)
The same applies for the small 620R.
Anyone guess the value of the single colour carbon rod resistor ? The second part is who can guess the measured value ?

richj
 

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The lower one in the photo someone pointed out was US MiL = correct. that reads 10R

So what looks like an orange band is really brown? 10 ohms on a meter?

The blue (is it really blue?) band is not a US military designation. This is what is strange. This may be a UK military resistor. I don't know where to get the carbon spec from UKMOD. They may be also published under NATO.

Is that a white band, instead of blue? MIL-R-22684 metal films, RL20, use a white fifth band as an identifier. TRW made them in brown molded, I have a few.

I have some more comments, but first I want to search for NATO docs. I have seen them before.
 


Here is a pic of three types of color-band military resistors.

The top one is and RCR20 (carbon comp-slug type element) with orange fifth band. Orange means failure-rate R. This type could also have a yellow band.

The middle one is a TRW RCR20 (carbon comp-the type with the glass tube inside) with yellow fifth band. Yellow means failure-rate S. S is the best of the failure rates.

The bottom is an RL20 semi-precision metal film Mil-R-22684. The white fifth band is the unique designation for this type of mil resistor. This is the only place a fifth white band is used on a mil-resistor in USA.

If your fifth band is really blue, and not white altered by the flash of the camera, then you have something that is not from USA. As far as I have ever seen, and I think I have seen all types.
 

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I have identified the resistor with the blue fifth band.

The wide first band does mean wirewound.

It is an IRC 1W flameproof wire, SP20F. The 1995 IRC catalog says it is the size of a 1/2W.

The blue band means flameproof.

The resistor above it has a wide blue band for the first band. This should also be a wire.

I also found a book that says a carbon comp with a wide green fifth band is tested for "load cycling."

It is my opinion that the color code system (for all types of parts) was abandoned primary because some companies didn't strickly follow it. The complexities of the codes established by industry were bad enough, but many companies made their own unauthorized revisions to the codes. The colored coded diodes are an impossible mess.

There is an established color code for radial dipped tantalums. I found over 6 different changes to it by manufacturers in their literature. Unless one has the manufacturer, which is not on the color-coded part, the code is not reliable.
 
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