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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On 2/8/2025 9:58 AM, Steve G8GSQ via groups.io wrote:
In general I'd say use metal film for everything. In this case, maybe consider carbon film and don't overdo the power rating. If the resistor burns out it might just save the tube; metal film can usually take a lot of overload.
The T4 I've just been working on had run just fine for years with 18ohm (2W metal film) resistors until operator error took them and the tubes out.
I think the exact value isn't critical. 2 x 33R 0.5W is a simple option.
Steve G8GSQ
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Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
