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RE: What tubes to use with this Interstage Transformers?

"A simple 1st Order RC filter will filter at 6dB/octave or the 20dB/decade beyond Fc. It doesn't matter how much current you are supplying at Fc because Voltage will just be attenuated due to the Xc. The ONLY THING to reverse is to supply a bigger Vin to negate the roll off or uses a local feedback to reduce the gain (thus changing Ctotal value to shift the Fc)."

That is not true. A lower drive impedance means the Fc is shifted higher, out of your way. That fixes the problem at it's core.


"The drop is 3dB at Fc. So, ideally we want to see Fc at 20KHz or beyond. If Fc is at 20KHz, the FR roll off probably starts at around 18KHz. "

One octave below the Fc is the -1db point. So a Fc of 20kHz means you are still -1db at 10kHz.


The phase is disturbed for a decade.

So, ideally we want to see Fc at 200KHz or beyond.

That is why, for a low pass filter, if you want 20kHz undisturbed you need the -3db point to be 200kHz.

And at the other end, for a high pass filter, if you want 20Hz undisturbed you want the -3db point to be 2Hz.

All of that aside, you should look closer into Miller capacitance and what it takes, current wise, to drive shunt capacitance.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

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