Shown above is the complete tube headphone amplifier. The amplifier provides a clean output signal and low output impedance without a global feedback loop. And yes, 6H30 triodes could be instead. And no, I will not provide the cathode resistor values for the 6H30 tube, as on the www.glass-ware.com site there is a link to a free download of the Live Curves program for this tube and determining the resistor values is an excellent homework assignment.

Conclusion
    While we only scratched the surface, we had to start someplace. What was left out was circuits like phono preamps and electrostatic direct drive amplifiers. (We could try to create an inverse pre-distortion signal by loading the driver stage with an inductance in series with a plate resistor, as the output would be loaded by a capacitance in parallel with a plate resistor.)
     As always, if you build any of these circuits, please give us some feedback on your results.


                                //JRB

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