Yes, exactly. The 12AU7 model includes only one-half of the heater (pin H1 & H2 in subckt model). Therefore the current through it should be designed to be about 150mA. Indeed the ratio 1.25/7.5 for LM317 in "current source" configuration is 166 mA.
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On Tue, Feb 18, 2025 at 08:53 AM, Jerry Lee Marcel wrote:
Actually, it is not "driven" by a current source.
It is rather "biased" with a current source, which is a perfectly legit way of operating a 12AU7.
The actual signal source is a voltage source.
Since only half of the dual triode is used, it's rather normal to use only one-half of the heater, hence a 6V connection. Again a quite common arrangement.
UIC flag for .TRAN analysis skips the initial DC operating point solution step (aka ITS). All energy storage components (i.e. capacitors & inductors) by default start transient with 0 stored energy.
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Therefore, do you think that the difference w.r.t. .TRAN without UIC comes down to the fact that in the latter the initial ITS step picks as stable operating point a nonsensical one for the 12AU7's heater (as you said where the 12AU7's heater generates energy from (very) thin air) ?
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On Tue, Feb 18, 2025 at 07:16 AM, Andy I wrote:
With UIC, and no other changes:
Normal solver -> 1.165 V @ 186 mA into the heater.? That's somewhat better.? But still not right.
Alternate solver -> 1.165 V @ 186 mA into the heater.
Carlo