SoundMods wrote:
Randy -- with all due respect -- I have been talking about cathode current. Power tubes in my experience have a "sweet spot" with regards to the cathode current and I have found that it is not the maximum current the tube can tolerate. That said -- with fixed bias you apply a negative voltage to the grid. The higher the voltage the lower the current through the tube. The lower the voltage the higher the current. OK? With cathode bias (preferred by the late Sid Smith) the voltage drop across a cathode resistor (say about 300-ohms as a possible example) creates a positive voltage with respects to the grid potential. The cool thing about cathode bias is that it "tracks" the music flow. Many arguments out there discuss the benefits of both methods. The French company Jadis has used an old G.E. trick using both methods together. A negative voltage on the grid as a starting point together with cathode bias.
Correct me if I am not right, but the less negative the grid to the cathode, the more of the electron cloud can pass thru the grid to the plate, thus increasing the current flow to the plate as current is a measure of the number of electrons flowing in a circuit, and thus the more power dissipated in the plate. The cathode current is the sum of the current flow in the plate and any current flow in the screen grid, there should be NO current flow in grid 1, the current flow in grid 2 a good bit smaller than the plate current. Assuming that you are operating on the linear portion of the load line for the grid voltage you are using, you will get a linear result of the amplification from the tube, operating in a non-linear portion will add non-linearity to the amplified signal. As far as cathode bias tracking the music flow, I believe that is the whole point of amplification. Whether you let the cathode biasing track the music or grid 1 track the music, the resulting signal should be the same if linear amplification is desired.