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cathode resistor, which would serve to better approximate a current source, but would do nothing to increase the idle current limit to the negative current swinging of the Cathode Follower.

The White Cathode Follower
   Mr. White's improvement on the Cathode Follower was to create a buffer that boasted a much lower output impedance and the ability to sink as well as source current, i.e. push-pull operation. The lower output impedance results from the use of a feedback loop from the plate resistor to the bottom tube and the use of two tubes allows the buffer actively to draw current in both directions.
   Because of the increased complexity of the circuit, the math is much more complicated than that of a simple Cathode Follower:

White Cathode Follower

   As an example, given a setup that consists of a 6DJ8 with a bypassed cathode resistor of 200 ohms and a 10k plate resistor, the results are     
    Gain = 0.97
    Zo = 3.44 ohms
    PSRR = -65 dB.

   Gain =               muČ + murp/Ra                           
                (muČ + mu + 1)  + (mu+2)rp/Ra

   Zo  = 1 / [   (1 + mu)/(rp + Ra) + 
1 + mu(mu + 1)/(1 + rp/Ra)
                                                                 ((mu + 1)Rk + rp)               


    PSRR =                                             2rp + (2mu + 2)Rk
muČ+mu)Rk] [(Ra+rp)/(mu+1)+rp+(mu+1)Rk)/(muRa)]

pg. 4

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