I'm trying to learn anode and cathode load line plotting Google style and have one small question... Some of the tutorials tell you to sum the value of the cathode and plate resistors in computing the current, and other tutorials neglect to even mention this and just tell you to use the value of the plate resistor. It doesn't seem to matter much with maybe a 12AX7 where the cathode resistor might be 1K and plate 100K, thats only a 1% difference.
Is it best practice to routinely just sum Rk and Rp so the total current across the tube is accounted for?
Is it best practice to routinely just sum Rk and Rp so the total current across the tube is accounted for?
Yes, since the cathode is the reference point for all the tube curves. Then the plate and cathode resistors
are indirectly in series and add.
are indirectly in series and add.
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I suspected that, then Id say nearly half the folks teaching load lines on the Internet are not summing in Rk.
No they aren't, but the accuracy is loose enough that it makes only a small difference in many plots,
especially for high gain circuits.
Classically, load line plotting was taught for tubes with a grid battery instead of a cathode resistor,
so there was no cathode resistor in the circuit to consider. Ironically, some have gone back to fixed bias,
often with an LED in the cathode circuit.
especially for high gain circuits.
Classically, load line plotting was taught for tubes with a grid battery instead of a cathode resistor,
so there was no cathode resistor in the circuit to consider. Ironically, some have gone back to fixed bias,
often with an LED in the cathode circuit.
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