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.
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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.
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I think the exact value isn't critical. 2 x 33R 0.5W is a simple option.
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Steve G8GSQ
