In the above circuit we see a grounded-grid amplifier cascading into a cathode follower. The coupling capacitor may seem too large in value, where in fact it is probably too small in value. The grounded-grid amplifier's input impedance is equal to the sum of the rp and the plate resistor divided by mu +1:
      Z_in = (R_a + r_p) / (mu +1)
Given a 6DJ8 as the tube, the input impedance equals 380 ohms in parallel with the cathode resistor's 200 ohms (about 130 ohms). The low frequency cutoff is found by the following formula:
       F_low = 159155/(Z_in + Z_cartridge)/C
So in this example, 50 µF equals a -3 dB cutoff frequency of about 25 Hz. Using a higher rp tube such as a 6072, 5751, or 12AX7 would increase the input impedance, but at the cost of more noise. (The usual compromise is to use an electrolytic capacitor in parallel with one or two high quality film caps.)
      The grounded-grid amplifier allows an easy noise canceling trick, as a small quantity of power supply noise can be injected at its grid, causing an inverted noise signal to appear at its plate, which then mixes and cancels with the power supply noise there in much the same manner as it did in the cascode noise-nulled circuit. 

Bootstrapped Compound Amplifier
     This sleeper of a circuit was described in length in the "SRPP Deconstructed" article from earlier this year. In a nutshell, this circuit works to magnify the first triode's plate resistor, making it effectively much larger, so that the gain from the first stage can nearly equal its mu. The tradeoff is that the second stage no longer has a  low output impedance similar to a cathode follower. Still, this deserves a second look.

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