azazello wrote:
300B has bias 30-50v and for driving it is need mu 40-50. 6SN7 is suitable in SRPP only!
But GM70 has bias more 100v and mu must be 150. I'm afraid that 6SN7 isn't suitable.
/Aprox. You can choose tube with mu = Ubias next power tube divide Uinput ....
P.E. mu in.tube must be = 100v GM70 divide 0,6-0,8v = 166-125 ....You can use for driving GM70 only penthodes with current 30-50 ma/.
I don't quite understand how you compute the input power needed to drive the GM70.
How would you model the GM70 as a load? A capacitor? A capacitor in parallel with a resistor?
Take a look at the data sheet, tell me what the input impedance of the GM70 is, and I'll tell you if the 6SN7 SRPP will be able to drive it. I admit my ignorance here, but certainly a prerequisite for a driver stage is voltage swing. I repeat, the gain, the current and the power don't mean a thing if the driver tube can't handle the voltage. Conversely, the voltage swing doesn't mean much if the driver output impedance is too high to drive the power stage.
My problem is computing the input impedance of the GM70. The input capacitance on the grid is pretty clearly defined. I guess my sticking point is "how can a tube transfer
power to another tube if tubes draw no appreciable grid current?"
The models I've run in PSPICE indicate the 6SN7 SRPP could drive at least several times the input capacitance of the GM70 without any ill effects.
I think there's too much of a language barrier here. I have trouble understanding your posts. Nobody's fault - it is what it is.