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• Is there a specific type of resistor composition that you prefer to replace these with??
• Recommended to upgrade larger than 1W??

Carbon film will run at red heat without damage. I spent some of my wasted youth working for a resistor manufacturer. We made established reliability metal film and mil spec carbon film resistors.
Otherwise I agree. There are oxide coated composition resistors which work well for this sort of application. There are very few virtues to old type carbon composition resistors. They were very widely used for a couple of generations because they were cheap to make. Laser trimming of carbon and metal film has reduced production costs to the point where they are now quite cheap.

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Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

One watt is enough. Modern carbon film will do fine, they do not drift. Metal film will also do fine. I think Garry used to recommend oxide coated film. Since the drop is part of the measurement of "plate" current (actually cathode current) the value is of some importance.
Old fashioned carbon composition resistors were never better than 5% because the heat of soldering them could cause that much drift.

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Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

As I mentioned I worked for a manufacturer of carbon and metal film resistors many years ago. We made MIL spec carbon film resistors. They were NOT delicate or fragile. Bot types got tested for strength of leads, we used two methods of fastening leads, swaged end caps and epoxy conductive paint. Either type would take tensil strength tests that would pull apart the ceramic forms before thee leads came loose. Carbon film were generally painted with epoxy and baked, metal film resistors could be painted or molded, depending on application. Carbon film resistors will run at red heat without being destroyed. Sine the general construction of both types is similar there is little difference in strength and resistance to mechanical damage. '
Our carbon film resistors were made by pyrolityc deposition. Prepared ceramic cores were subjected to a flow of carbon monixide gas in a fused quartz jar under yellow heat. The jar was tumbled during exposure to the gas. The thickness of the coating depended on the time of exposure. Once coated the leads were attached and the blanks were adjusted to the correct value and went through a series of tests before coating and final testing.
The metal film resistors being established reliability parts, went through more extensive testing and were generally adjusted to must closer tolerances. The company also made wire wound precision resistors but I have much experience with them than the coated types.
I should add that the metal film parts were made by vacuum deposition, the characteristics of the resistors, such as temperature coefficients, being determined by the mixture of metals used and exact details of the evaporation (trade secrets). I think both kinds are now spiraled and trimmed by laser rather than the carbide and diamond saws we used but this was long in the past.
In any case deposited carbon resistors are NOT mechanically delicate and are generally difficult to damage.
FWIW, metal oxide film resistors are excellent for some applications.
A final note: film resistors are no more reactive than carbon composition resistors. In fact, they generally have superior RF characteristics. A good instrument for testing them is the old Boonton 250 RX-Meter but there are many more modern impedance meters that will prove this out.

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Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

Carbon comp resistors are sensitive to moisture as well as heat. The resistance to moisture depends a lot on the quality of the housing. About the best of the CC resistors is either Allen-Bradly or Ohmite. They are the same, the resistors were made by AB and marketed by both companies and are recognizable by having the values in both color stripes and printed in ink on the body.
CC resistors were made by a great many companies, including IRC and Stackpole. In general resistors with seams in the molded bodies will be found to have drifted significantly.
CC resistors were never made in tolerances closer than 5% because just the heat of soldering them can most them that far.
While they are supposed to have some advantage for handling pulses I don't think that makes a difference for most applications. For them most part they should be avoided as either replacements or new work.
CC resistors are made from a slurry of granulated carbon in a carrier of an insulating material with a binder. Drift depends on absorption of moisture and heat. It is not moisture alone. Heat can change the way the carbon particles contact each other in a non reversible way. I was never involved directly in making them so don't know the details. In the industry they were called "mud" resistors. While they are supposed by some to be superior for RF applications it is a myth as measurements will demonstrate.

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Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

I think both kinds are now

spiraled and trimmed by laser rather than the carbide and diamond saws
we used but this was long in the past.

*** I worked for a telephone equipment manufacturer in the mid-70's. We had a rig for laser-trimming surface mount resistors on hybrids( small circuits assembled on ceramic substrates ).

- Jerry, KF6VB