Carbon composition versus carbon film resistors!

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Carbon composition versus carbon film resistors!

Post by nunu on Fri May 15, 2009 11:15 pm

I started repairing an EICO 950B bridge capacitance analyzer most resistors are the older carbon composition type, am having a hard time finding some older resistors

Can I replace them with the newer carbon film type without compromising the performance?

Thanks.

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Re: Carbon composition versus carbon film resistors!

Post by Bill Cahill on Sat May 16, 2009 12:18 am

If they are regular resistors, and, bad, yes. If they are precision resistors, NO.
Precison resistors are those of 2 percent tolerance, or, less.
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Re: Carbon composition versus carbon film resistors!

Post by Resistance is Futile on Sat May 16, 2009 3:55 pm

Make sure they are not wire wound. Wire wound resistors have a wider first color band on the older resistors, and on the newer ones usually the words wire wound or ww. And usually precision resistors are printed values vs color bands, not always though. Some still used the tolerance band of silver, gold, and colors such as red for 2% brown as 1% for the fourth band and temperature as the fifth band.

Carbon film resistors vs Carbon resistors will work just fine wattage for wattage.
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Re: Carbon composition versus carbon film resistors!

Post by Dean Huster on Wed Sep 02, 2009 7:55 pm

Carbon film resistors vs Carbon resistors will work just fine wattage for wattage.

Let me fine-tune that statement a bit. It's accurate when you're considering average power. However, you'll find that a carbon composition resistor will handle big power spikes of one or two seconds duration because of its heavy bulk. There's not much to a carbon film's element and a power surge will wreck them.

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Re: Carbon composition versus carbon film resistors!

Post by Resistance is Futile on Thu Sep 03, 2009 7:58 pm

most circuits don't have big power spikes, the ceramics that film resistors use would absorb any momentary increase in heat without failure. most military gear uses film resistors to replace failed carbon resistors, for that very reason. In the NTDS HI Voltage power supplies (area 18 PS), the circuit cards were a constant problem with carbon resistors. There were 40- 220 ohm carbons in series that would burn up the fiberglass boards underneath and burn the traces and holes around the leads, requiring major circuit card repairs.

The Idea of using film resistors and elevating them off the board by 1/8 inch was proving successful, another problem was the resistors were conformal coated to prevent moisture from causing -arcing. That also lowered the heat dissipation capacity to where the resistors would burn up. The conformal coating wasn't applied to the film resistors. also the New resistors had a 7 Watt rating instead of the 5 watts. And the film resistors were mounted with the end caps that had four tiny holes around the circumference of the cap.

No further problems, Note:
The film caps were the same physical size as the carbon 5 Watt.

Tells me, through my experience that film resistors are a better way to go, as they have tighter tolerances and can handle heat better.Wink
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Re: Carbon composition versus carbon film resistors!

Post by Bob Masse on Sun Sep 13, 2009 7:11 pm

Hi! Carbon Comp resistors are available at Surplus Sales Of Nebraska and justradios@yahoo.com.If you just google either name the links come up.Hope this helps. Bob

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