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Resistor Composition


Posted on Tuesday, August 24, 2004 - 02:15 pm:   

Doing a power section rebuild.
Old carbon comp resistors in there.
Mouser dont have 1w or 2watt'ers.
Xicon dont make a 2 watter.
Do they have to be old CC's?
What do you reccomend.

Steve Kennedy
Posted on Tuesday, August 24, 2004 - 04:48 pm:   

Carbon comp resistors are absolutely the best replacement for carbon comps in amplifiers.

Carbon film may be lower noise but they are are simply a film on the surface of a chunk of ceramic, while carbon composition resistors are a complete medium for signal and power through & through ("solid-state" so to speak).

Try these:

Surplus Sales
Torres Engineering

You might have to look hard for the correct resistance value but they are still out there!


michael kaus
Posted on Wednesday, August 25, 2004 - 10:38 am:   

i usually use metal resistors in the power section. They seem to hold up better and if you're using the 1 and two watt versions on the tube sockets, they seem to resist heat better. Just my 2 cents worth. Mike.
Steve Kennedy
Posted on Thursday, August 26, 2004 - 04:50 pm:   

The film resistors exhibit a higher capacitance and/or inductance than carbon comp due to their construction. While the ceramic film resistors are better as far as heat goes, their increased capacitance can change the tonality of the power section somewhat if used in a location that passes audio through it (and to a smaller extent plate power).

Not always noticeable but just one of the reasons why carbon comps are typically specified for "audiophile" tube amps and film resistors are avoided. Similar preferences are at work in the "film cap" vs. Electrolytic caps in audio circuits, but the film caps usually win that battle!


Posted on Thursday, May 26, 2005 - 05:36 pm:   

Hi. Do these resistors age and need replacement? I am contemplating cap replacement on my amp - do I need to have the resistors replaced as well?
Steve Kennedy (admin)
Posted on Tuesday, May 31, 2005 - 05:17 pm:   

Unless a resistor has been cooked (dark discoloration) or burnt, it is probably OK.

Just on general principal, I would replace any resistor living on top of a tube socket for 25 years! The one drawback to Carbon Composition resistors is that they can develop cracks and will cause popping and other assorted noises that can be hard to trace. This is an area that Metal Film resistors excel... they are extremely quiet by comparison.

With the amp on and operating (and one hand in your pocket to prevent DEATH), lightly tap the large carbon comp resistors around the output tubes with a wooden stick or other non-conductive probe and listen to the output for noises that could indicate it is time for a replacement.


(Message edited by admin on May 31, 2005)