[Nick Poole] does a lot of custom work with vacuum tubes — so much so that he builds his own vacuum tubes of various shapes, sizes, and functions right on his own workbench. While the theory of vacuum tubes is pretty straightforward, at least to those of us who haven’t only been exposed to semiconductors, producing them requires some specialized equipment. A simple vacuum won’t get you all the way there, and the complexity of the setup that’s needed certainly calls for some automation.
The vacuum system that [Nick] uses involves three sections separated by high-vacuum valves in order to achieve the pressures required for vacuum tube construction. There’s a rough vacuum section driven by one pump, a high vacuum section driven by a second pump, and a third section called the evac port where the tube is connected. Each second must be prepared properly before the next section can be engaged or disengaged. An Arduino Pro is tasked with all of this, chosen for its large amount of ADC inputs for the instrumentation monitoring the pressures in each section, as well as the digital I/O to control the valves and switches on the system.
The control system is built into a 19-inch equipment rack with custom faceplates which outline the operation of the vacuum system. A set of addressable LEDs provide the status of the various parts of the system, and mechanical keyboard switches are used to control everything, including one which functions as an emergency stop. The automation provided by the Arduino reduces the chances for any mistakes to be caused by human error, allows the human operator to focus on other tasks like forming the glass, and can also react much faster to any potentially damaging situations such as the high-pressure pump being exposed to atmospheric pressure.
As you can probably tell, [Nick] is pretty passionate about this stuff — last year he gave a talk at the Hackaday Supercon that went over all the intricacies of building one’s own vacuum tubes.
Briefly, the process is to first bake the pine cones to remove any moisture. Then they get coated in a heat-activated resin for stabilizing, which is a process that infuses and pre-seals the pine cones for better casting results. The prepped pine cones go into molds, clear resin is mixed with coloring and poured in. The resin cures inside a pressure chamber, which helps ensure that it gets into every nook and cranny while also causing any small air bubbles introduced during mixing and pouring to shrink so small that they can’t really be seen. After that is cutting, then sanding and polishing. It’s an excellent overview of the entire process.
