Quote:
Originally Posted by kalee20
To be fair, you can get an equivalent power gain from just ONE device, a power MOSFET operating in Class A... which you can use a 22MΩ gate-tie resistor with.
|
Yes, but to be very fair, both the EF98 and the OC16 are pre-1960 technology.
And, not only that, your power mosfet has an input capacitance many orders of magnitude higher than the grid capacitance of an EF98. The mosfet requires a lower Z source impedance to drive the gate, than with the EF98, if you want to maintain the high audio frequencies. It is is much more friendly looking into the grid of a pentode like the EF98 than into the gate of a power mosfet. The G1 of the EF98 just looks like your 10M resistor, the gate of the power mosfet looks like the 10M plus a parallel 500 to 5000pF capacitor in parallel, depending on the power mosfet type.
The G1 capacitance of the EF98 is 6.7pF and G1 is isolated by the screen grid action of the pentode construction eliminating the Miller effect too. If you can find a power mosfet that does that, I'll buy into your argument !