#6SN7 CATHODE FOLLOWER SERIES#

(Having mentioned the darling topology of tube audio, I should, if only in passing, that the grounded-grid amplifier can be SRPP-ed by adding a second triode atop the plate resistor, which is just what Bruce Rozenblit did in his 'grounded-grid amplifier.') The first obvious addition would be to follow the grounded-grid amplifier with a cathode follower, which would offer a low output impedance and shield the grounded-grid amplifier from the external load. Believe me, if the twin-triode tube did not exist, the SRPP would not be as popular as it is. Since most small-signal triodes usually come in pairs, such as the 6DJ8, 6SN7, 12AU7…, we always face the problem of what to do with the second triode. This is the atomic grounded-grid amplifier, which then can be incorporated on more complex topologies.

#6SN7 CATHODE FOLLOWER SERIES#

If there is a series resistance, Rs, then the formula becomes: Thus, the formula for the AC voltage gain of a grounded-grid amplifier isĪssuming no series resistance. Where the grid's transconductance is given by One interesting feature of the grounded-grid amplifier is that it offers a slightly higher gain than the comparable grounded-cathode amplifier, as the cathode offer a slightly higher transconductance than the grid. On the other hand, if the cathode resistor terminates into the signal source, rather than ground, then the formula is: Where || stands for in parallel with, such that a || B equals (a x b) / (a + b). How low an input impedance? Where a grounded-cathode amplifier offers, at audio frequencies, an input impedance roughly equal to the resistor that connects the grid to ground, the grounded-grid amplifier's input impedance is equal to: Indeed, its use in audio circuits has been rare, being limited by it comparatively low input impedance.

Because of its better high-frequency response over the comparable grounded-cathode amplifier, the grounded-grid amplifier has found its widest use in radio designs. The result is no phase inversion of the input signal and much higher high-frequency bandwidth, as the cathode is shielded from the Miller-effect capacitance by the grounded grid. The real grounded-grid amplifier is a simple affair: the grid is grounded, if not directly to ground, at least AC 'grounded' via a capacitor to ground the cathode receives the input signal, either directly or via a resistor or capacitor or coil and the output is taken at the plate, in the same as it is in the grounded-cathode amplifier, where the plate meets the plate resistor, Ra. How so? I often receive e-mails that ask about the grounded-grid amplifier and I must figure out if they really mean the circuit shown below, which uses one triode, or the cathode-coupled amplifier that Bruce Rozenblit designed, which uses three triodes. If there is a 'real' grounded-grid amplifier, is there then an 'unreal' grounded-grid amplifier? Yes, indeed, which is a nuisance and headache for someone like me.

6sn7 cathode follower