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Re: Saaaay...

Doug wrote:

::::The load seen by each triode certainly does vary a bit. In the RDH3 an equation is offered which relates this change to plate resistance(for Triodes ). I am not sure I buy the whole thing.::::

As John Broskie points out... there is no intrinsic pri impedance. Pri impedance is determined solely by the load placed on the secondary and the turns ratio btwn the primary and secondary windings.

impedance ratio equals (n1\n2)^2

in pp each half pri's impedance ratio would be ((n1/2)\n2)^2

thus if the load on the secondary is 600 ohms and we have a 4:1 turns ratio (a 16:1 impedance ratio) from full pri to sec then the primary impedance will be 9600 ohms.

each half primary will have turns ratio of 2:1. Thus an impedance ratio of 4:1. Multiply this impedance ratio by the load on the secondary and we get an impedance of 2400 ohms for each primary half.

A tube or tubes, a generator or generators each work into the primary impedance they don't "make" or "define" the primary impedance which is determined solely by the load on the secondary and the turns ratios btwn the primary (or any sub-portion) and the secondary.

Thus, this is why, we can "ratio" transformers and change the primary impedance... simply by changing the load on the secondary winding.

The generator or tube may be more or less happy working into a given primary impedance... it may load the generator more or less than an alternative value of primary impedance... and the generator may develop more or less distortion operating into a given primary impedance.... but the generator or tube "sees" this impedance as it's load and works into this impedance... the generator or tube does not "define" or "make" the primary impedance.

as regards the behaviour of the tube and it's plate resistance and the "movement" of it's plate resistance... Steve Bench addresses this issue in his article on PP loadlines. I put a hot link to his text below.

msl




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