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RE: grid resistors first stage of amp

Jim is spot on about the 1:10 rule. We want waveform fidelity, not power transfer in small signal situations.

Another factor to take into account is Miller capacitance. The 470 KOhm parts previously mentioned are fine with a pentode I/P stage, but can easily cause HF info. to be rolled off, with a 12AX7 section in the I/P stage.

Modern, digital, sources will drive a 10 KOhm load, as that's an IHF "standard". FWIW, I use voltage followers in my designs to do that too. The old standby of a 600 Ω line impedance did not come into being by accident. ;>)


Eli D.


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