@cetoole was visiting, so we made a slightly absurd amp using parts from the bin.
I had originally milled the chassis with the intention of building a 6E5P triode -> 4P1L triode SE; then realized that would be a bit awkward, since the 6E5P is rated for higher dissipation than the 4P1L. I may have also forgotten that 4P1L filaments need power supplies when I bought my power transformer, too, so that was a non-starter.
Not wanting to leave two unused holes in the panel, the obvious solution was to throw some 0C3s in. Glow tubes are pretty; it follows that any amp that uses them will sound better than one that does not. A normal person might be tempted to string them in series and use them as a reference for a regulator. Instead, each channel gets its own shunt regulator with a voltage reference made up of a zener stacked on top of the glow tube, and a SiC shunt device. R7 ensures that the tube strikes.
And the current source (which is nothing inspired)
The regulator terminates into the cathode rather than ground, keeping the cathode regulator out of the output current loop. It also forces the PNP to run at constant current regardless of cathode current, meaning its impedance will also be constant.
It sounds like a single ended triode (i.e. terrible). But it was an awfully fun build. Slightly tempted to parafeed or otherwise upgrade the iron. It's surprisingly silent when nothing is playing.