Audio advice and discussions with audiophiles and professionals. Free discussion forums, open to all and frequented by industry experts. Ask questions and get advice on stereos, speakers, hi-end amplifiers, pre-amps, home theater, tube hi-fi, turntables, vinyl, tweaks, music, films, video, DVDs and more.
I mean the grid to ground impedance not the grid resistor. I assume this impedance is in series with the grid resistance. I have always considered a tube grid to be an open, aside from the interelectrode capacitance.....Tube cad says no. What I'm trying to do is install a high pass filter between the output of my preamp and the input of the power amp. Thanks...Tre'
Re: What is the input impedance of a 6sn7?
In normal operation (grid negative to cathode), input impedance of the 6SN7 triode (g1-ground) is close to infinity, or at least, very high. Then grid-leak resistor (say 220k from g1 to ground) is actually our input impedance (220k in parallel with >>220k = 220k). We have the "problem" with input capacitance (Cgk+Cstrays+Cmiller), say about 100pF for 6SN7. The easiest way with filter stages is to observe triode input like, say, 220k in parallel with 100pF.
Thanks Damir. I was reading TubeCad wrong. It's redundant. It's states the F-3db point for a given circuit and then states the capacitance reactance in ohms as the Zin. Knowing the source inpedance and the F-3db point I can calculate the CR but the program gives it anyway. It just does not make it clear. Naz helped me with this. Thanks....Tre'