Introduction to "Valvalyzer" a Windows workstation vacuum tube and stage simulation software package written by Jim Reese from AmpCad.com

[Aridace]

@jimreese What you are missing is the physically impossible screen voltage of 697.767 Volt NEGATIVE.
The circuit is supposed to be a low distortion 20 dB preamp.

 

[Ray Waters]

I'm curious. Have you built this circuit to see if it actually performs as a "low distortion 20 dB preamp?"

 

[Aridace]

No, before building anything I thoroughly investigate the circuit via sims. Extremes get much attention and I discovered the issue increasing the screen grid resistor to 22 meg. That's not optimal because the DC value at the cathode follower should be ~0.5 Ub. My suspicion started when lowering Ub of the circuit below to 200V, to accommodate Vfk of the 6F12P. At 300v, this THD sim and below, the circuit.