A test lashup to see how it all works, with an ersatz plate cap atop the IBM 21HB5A Beam Power tube on the far right end:
Those sockets must mount in a chassis, not flop around loose on the cable.
I hacked the code out of the Hard Drive Platter Mood Light; there’s a lot to not like about what’s left and I must rethink the overall structure. The colors now run an order of magnitude faster than the Platter Mood Light, with a 90° phase angle between successive Neopixels.
The mica spacers in the 12AT7 Dual Triode tube (second in the sequence, Noval socket) look cool & crystalline:
When the red phase comes around, it becomes a firebottle:
With a touch of fire in its hole, the IBM 21HB5A Beam Power tube looks just flat-out gorgeous, despite that translucent blue plate cap:
Cool green works pretty well:
If you wait long enough, it’ll probably turn True IBM Blue.
This worked out even better than I expected!
The Arduino source code as a GitHub gist: