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RE: The road ahead

The Miller capacitance of a tube is the (static) grid to plate capacitance multiplied by the mu of the tube plus the (static) grid to cathode capacitance.

The output impedance of a resistor loaded driver stage is the plate resistance (at the operating point) in parallel with the plate load.

You used a lot of words to say very little.

"Certainly, the Miller Effect of the DHT being driven is also loading this stage, but I am able to get the bandwidth I need anyhow by carefully evaluating all of the factors that impinge on it. "

If you would just say what the output impedance of you driver stage is (and how you arrived at that number) and the Miller capacitance of your output tube we could settle this.

I don't see how the output impedance of a resistor loaded 7b4 driver stage can be low enough to prevent the Miller capacitance of a DHT from causing problems within the audio band.

You say you have done this, I say you can not have done this.

Unless you are willing to explain, in plain English, how you prevent this low pass filter from negatively effecting the audio band I will go on believing that it does.

I think that is fair and reasonable.

BTW You have said in the past that your amplifiers start to roll off at 15kHz. You also stated that with NOS tubes this roll off can start as low as 9kHz do to the increased Miller of some of the older tubes.

That sounds like an admission that the high output impedance of your driver tube is causing (in all cause, even with the new tubes that have lower Miller) problems in the audio band.

If, when you say that you get "the bandwidth I need", includes roll off and phase disturbance within the audio band, I would propose that the bandwidth you need may not be the same as the bandwidth myself and most everyone else needs.

Tre'


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


Edits: 06/24/12
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