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Attached is the plot of the conditions at the input of E180F at full output power.
Blue trace is cathode (at 2.15 V) and green is g1. The minimum g1-voltage is more than 0.5 V, so no problem is likely.
And if the grid current were a problem, the operating point can be shifted with 180 ohms cathode resistor to a place where the minimum g1-voltage is more than 0.77 V.
Actually this could be optimum, since the THD is decreased a bit.
And even more; with 1k the minimum g1-voltage is > 1 V.
With 1k, the anode current is still 12.3 mA.
Blue trace is cathode (at 2.15 V) and green is g1. The minimum g1-voltage is more than 0.5 V, so no problem is likely.
And if the grid current were a problem, the operating point can be shifted with 180 ohms cathode resistor to a place where the minimum g1-voltage is more than 0.77 V.
Actually this could be optimum, since the THD is decreased a bit.
And even more; with 1k the minimum g1-voltage is > 1 V.
With 1k, the anode current is still 12.3 mA.
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The R loaded, R//C biased E180F is good and simple solution...if you like "old style" tone.
The distortion not too low (for example over 0.4% at 150Vpp -this is about A1 region limit of this schematic), the driver output impedance is high, and increasing in HF region (below 100Hz).
Rout (without coupling capacitor):
3.9k 10Hz
2.95k 20Hz
2.3k 1kHz...100kHz
CCS loaded and LED biased schematic has lower (about 0.15% at 150Vpp) THD, and consistent output impedance (about 300R) in the whole 10Hz..100kHz region.
The distortion not too low (for example over 0.4% at 150Vpp -this is about A1 region limit of this schematic), the driver output impedance is high, and increasing in HF region (below 100Hz).
Rout (without coupling capacitor):
3.9k 10Hz
2.95k 20Hz
2.3k 1kHz...100kHz
CCS loaded and LED biased schematic has lower (about 0.15% at 150Vpp) THD, and consistent output impedance (about 300R) in the whole 10Hz..100kHz region.
An example/reference of this would be useful to see. Without it, is difficult to comment.
Especially how the output impedance drop from 3k of RC-coupled to one tenth (300 ohms) with CCS and LED-bias.
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Yes, that circuit will have low output impedance, but the output is not from the tube (as I assumed). It is buffered by a FET.
That circuit will surely outperform any tube-only-circuit, like the mu-follower with NFET I posted earlier.
But what is a surprise (to some), is that the RC-coupled circuit will give more linear outcome with 300B than an E180F with a CCS.
That circuit will surely outperform any tube-only-circuit, like the mu-follower with NFET I posted earlier.
But what is a surprise (to some), is that the RC-coupled circuit will give more linear outcome with 300B than an E180F with a CCS.
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