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RE: It has been planned to use individual cathode bias R

I made a model for the triode KT90 and this is what spice says happens. All of the info is in the pictures.

The individual WE 300B and EI KT90 curves. Grid voltage is from 0 to -110V



Green Lines represent the composite curves of the two if driven from the same voltage.



This is the above pic zoomed outwithout the KT90 to see that the composite lines actually become the 300B lines at some point. (looks like a nice even order harmonic generator)



In the below plots, the 300B is biased from 0 to -110V in 10V steps and the KT90 from 0 to -55V in 5V steps (note the voltage divider on the grid of the KT90. These are the two tubes by themselves.



And the two discrete curves with the composite curves added.



If you build the amp it would be fun to put a volume control (or balance control) on the grid of the KT90 to use as a "tone control" so you quickly play with the various sounds.

dave




Edits: 06/06/12

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