Carbon Composition Resistors
 

Does anyone have a source for 2 watt carbon composition resistors? Sources like Allied Electronics and Mouser Electronics just have up to 1 watt.

Thanks
konrad

Hi Konnie - I don't have a source, but I'm curious - do you need them to duplicate the appearance in something?
-Wayne B

Tubedepot has a pretty good selection. $2.95 each.

Murray

Carbon Composition Resistors
 

Hello Wayne B, I need them not for appearance but for functionality. Carbon Composition are the only type resistors that will take high voltage arcs. Film types will track across their surface. This is based on 40 years experience in TV design of high voltage circuits.
konrad

Carbon composition resistors
 

Thanks for the lead Murray. Unfortunately at that price and the amount of these used in the old 7 inch sets I would be broke in no time.
Konrad

Will wirewound resistors work? Jameco has a great selection of 5w wirewound ceramic resistors for 36 cents each. Mostly lower values though - I think the highest value I saw was 3k or so. I never heard about an application where carbon film resistors were inferior to the old carbon composite resistors. But I do know how the carbon composites like to drift...

What about metal film?

-Ian

Lol. I needed a close matched pair for a tube amp and bought 4 or 5 12k I think and couldn't get close enough. Gave up and used metal film.

Murray

I doubt you will do much better than that. I have bought several 1 watt "Ohmite Little Demon" carbon comps from Digi-Key, and they were right around two-dollars. Those are still in production. I suspect 2 watt is not. Good luck.

John

What are the max working voltages of most types of resistors. I've always read that standard carbon were good only to 500V, true?

Lefty

I don't remember, but I think that is correct. I think the 500v is for half watt, and that is the reason you dont see many 1/4 watt carbons in tube equipment (250v?). It goes up with wattage. sometimes they are strung in series to put less potential across each resistor.

In the old days, I think carbons were often pressed past these ratings.,That, the lack of inductance, and carbon comp's ability to take fairly high current surges without damage, are 3 reasons it might be a good idea to put carbon comp back in equipment that was designed around carbon comp.

Someone (Ohmite maybe?) makes some funky carbon-ceramic things that are supposed to replace higher-wattage carbon comp. I havent tried them.

John

I remember there used to be a type called "RCA Flameproof Resistors" and the body was blue. These seemed to be high quality and did come it 2 watt size I think. Am not sure what these used as a resistance element though,

The blue "flameproofs" I use are WW. Murray, On the matching of CCs, I've heard it helps to bake them in the oven at the lowest setting overnite. Never tried it though.

I tried that but they didn't taste any better.

Murray

I can get you ceramic composition 2 watt resistors for around a buck and a half. Some more/some less. These resistors are replacements for the expensive carbon jobs. I can get you anything from 3.3 ohms to 1 meg. The 2 watt ceramics withstand up to 700 volts and utilize 10% tolerance. Hope this helps. PM if interested.

Dang, I'm going to have to raise our prices...we've been charging 95 cents a piece for surplus Allen Bradleys...

--Bob

Back in RF class in college we were told to use nothing but composition resistors in RF circuits, like RF amps, oscillators, etc. The inductance of the spiral of metal or carbon film resistors plus the capacitance end-to-end, and between the spirals in the resistor made them too likely to resonate all by themselves, with highly unpredictable results.

My feeble memory tells me that 1/2 watt carbons were good for 300V, and 2W were 600 or 700. (I wouldn't bet more than about 50 cents on my memory). Also, there are some reallly L O N G carbons out there, and I suspect they are rated at higher safe voltage. I have made chains of carbons when I wanted to work with higher voltages (like making my own focus dividers on a TV. {act of desperation to get it running}).

I think those blue RCA Flameproof jobs were metal film. I probably still have some in the shop. I should file one down and see.

Old carbon resistors may be way out of value, so be sure to check them. There was an article in QST magazine a few years ago about that, and I think the author baked them in an oven at low (140?) temp for a while to drive moisture out of them and try to return them to their origional values. If I remember right, he was only partly sucessful.

Thats my rambling for the evening.

Oh yeah! Dont you just love the smell of those things when they flame out? Takes me back to my childhood, when the house always smelled like burned carbon resistors. Mom hated that!