Hello,
I'm using ngspice to simulate a tube amplifier based on 12AU7 triode. Attached you can find a zipped folder with the main .cir file and the referenced libraries.
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Coming from LTspice, I can see there is some issue when running transient analysis using ngspice. Namely the Initial Transient solution (ITS) step from .tran 10n 10m analysis picks a DC operating point solution quite different than LTspice (the same as the .op analysis).
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ITS/DC operating point looks a bit weird, indeed the amplifier's output signal V(out1) isn't good at all.
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Can you help me in understanding why ? Thanks.
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Carlo.
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Carlo