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RE: If you need precision current bias of power tubes...

"A current source does not suit so fine in a (PP) power output stage.
Tube rectification always occurs when leaving class A operation and spice simulations show that a capacitor in parallel to the 'current source' (or the bias resistor) reduces total harmonic distortion.

If you configure the output stage as a LTP with a current source "tail" it never leaves class A. Granted, matching tubes is a "bitch" but it can be done. Sonically the result can be quite surprising for those who have never heard it before. I'm currently running four triode connected KT-120s in PPP off of a single current source @290mA.

"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln

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