Looking at the 6c33c data sheet it looks like with 120v on the plate I will need -40v on the grid for 150ma. My question is in practice about how reliable is this could I assume I would get 150ma +- 10% and will this figure change a lot during the tubes life. Actual the same question applied to if I use 150v on the plate and a 267 ohm resistor will I realy get about 150 ma as would be indicated from the data sheet?
It is somewhat doubtful you'd get exactly 150mA, but something close. Bias will change as the tube warms up (mine seem to bias higher when cold and then settle lower as they heat up) and likely as the tube ages.
Perhaps use a suitable potentiometer to set the bias so that you can trim to 150mA. This is what I did for my 6C33C SET. The current tubes in the amp actually biased quite close to 150mA (within 10mA), so I didn't have to trim too much.
Perhaps use a suitable potentiometer to set the bias so that you can trim to 150mA. This is what I did for my 6C33C SET. The current tubes in the amp actually biased quite close to 150mA (within 10mA), so I didn't have to trim too much.
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