Carbon Comp vs Metal Film

[rsumperl]

Greetings everyone
So, is there any advantage to using a metal film over a carbon comp? Are there places in an amplifier that I should not be using a metal film?

Thanks,
Ray

[SY]

Depends on the circuit position. If you need low noise and stability, a metal film or wirewound will be your best bet. For power supply decoupling and grid stoppers, carbon comp traditionally work very well.

[riktw]

never place wirewounds in a SMPS
metalfilm is good for low noise.
for the rest, just try it out

[Brit01]

There are some good deals on Holco and Allen Bradley on ebay uk at the moment.

[richwalters]

Originally Posted by rsumperl

Greetings everyone
So, is there any advantage to using a metal film over a carbon comp? Are there places in an amplifier that I should not be using a metal film?

Thanks,
Ray

Output stages; cathode current sense- 1-10 ohm often used in fixed bias. MF types eventually go high as they cannot handle peak transient currents. Use wirewounds for these applications.

richy

[Sch3mat1c]

Carbon comp has no place in any electronics. Surely you meant carbon film?

[rongon]

I just replaced some 2W carbon composition resistors I'd been using as plate loads on a 6SN7. Even though I'd paralleled a 47k with a 220k to get roughly 38k, and each resistor in each pair was rated for 2W, all had drifted high by different amounts. So much for my carefully matched values! Carbon composition resistors just can't take any heat without drifting way off value. They do seem to sound nice, though.

At this point, I only trust carbon comps as grid stoppers.

[Steve Eddy]

Originally Posted by Sch3mat1c

Carbon comp has no place in any electronics. Surely you meant carbon film?

Nothing wrong with carbon comps in most applications in electronics.

se

[Rodeodave]

MF resistors are usually made by deposition of a metal on a ceramic cylinder. To get the desired resistance a helix is cut into the metal film by a laser, so its basically a thin strip of metal running around a ceramic rod (which also makes them inductive). Due to the tight interspacing MF resistors have a limited voltage rating. So wherever you have very high voltages or a huge voltage drop you have to be careful with MF resistors.

[Rodeodave]

Originally Posted by Sch3mat1c

Carbon comp has no place in any electronics. Surely you meant carbon film?

Apparently carbon film has the worst of two worlds...inductive, high TC and low voltage rating, plus noisy.

Carbon comp virtually have no inductance and a high voltge rating due to the continuous voltage drop over the part.
MF have low noise and very low TC.

(TC is short for temperature coefficient)