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Do It Yourself (DIY) paradise for tube and SET project builders.

RE: "a 1 watt film resistor should do quite well"

But just like selecting a real fuse you have to evaluate the circuit!

You have to consider the current capability of the tube. I use 2 watt resistors in the Cit II with the KT-88s - for EL34s I normally use 1 watt. For EL84s or lower wattage tubes you can often get by with 1/2 watt. There is no single hard and fast rule...

But in considering the cathode circuit you must consider all the possibilities - bias current is not the only thing the resistor sees. Put a scope probe on the cathode pin of the power tube when music is playing - you'll see other waveforms too.

Too small a resistor and the resistor will pop unnecessarily.


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