Try using a 12U7 instead of a 12AU7. It's meant to operate at 12v. Also, 12v "space charge" tubes are great for this application.

Merlin Blencowe has instructions on operating triodes (and especially the 12AU7) at low voltages. His goal is linearity (to the extent that it's possible), so it's not as appropriate for a course on "distortion". His writings also suggest nontrivial grid current, which won't show up on the Koren model or most datasheets. It's better to measure an actual 12AU7 than trust online calculators so far from the intended range of operation.

True. The 12U7 tubes run at low voltages, but I've been fascinated with circuit topologies that run the big boys like 12AX7s and 12AU7s at low plate voltages. There's a kit called the "Tube Head" by Paia that runs 12AX7s at 12 volts (actually, there's a voltage multiplier inside to increase the plate voltage, but not very much). I built it and it sounds pretty good.

Thanks, Prof. Aaron 👍

omg I have dozens of those.

Have you used a transistor curve tracer to generate the plate characteristic at 12 volts? Thanks for the video. ps. I met Koren once in Boulder and we spent 30 mins talking about the modeling approach you mentioned.

Try a 12u7, without the "a", which is designed to operate at low voltages.

Fascinating video, Professor! Falstad is getting bettter at simulating weird things. I'm always a little puzzled when I see these 12V tube circuits. Is there a good reason not to power the plate with, say, a still finger-safe 48V? Does the low anode voltage give you some sort of magical distortion effect or something? (Yeah, I know, 48V is pushing 'touch safe' just a little bit, because my wife ran a manual PBX back in the day and said that the cords would give a nasty bite in wet weather. But 60 VDC or 25 VAC is legal by most codes even around children and livestock provided that the interrupter will break the circuit within 3 seconds of detecting fault current. If I recall, if the circuit is secured and GFCI protected, the limit is 120 VDC/50 VAC for adult workers, and obviously higher for trained workers with appropriate PPI.)

But did you actually build and test it!? (I feel like I'm taking crazy pills!)

At these prices, I'd expect these tubes to be fake, rather than real. Not that people likely to buy them will ever find out...

Electrons NEVER EVER flow from plate to cathode!!!