[m caldeira] a test tube needs to be tested, and there is no redundant equipment to carry out the old exchange test. He doesn’t have a test tube tester at hand. Inspired by a video in 2015, he managed to piece together a special test tube tester using things around the workbench. You can see the video of this process below.
To repeat his efforts, you need a few meters. Fortunately, they are relatively cheap these days. Generally, there is a way for the tube tester to adjust all the different parameters of the tube, but there is no reason not to use the test bench power supply to set these parameters.
Of course, this requires a high-voltage power supply. You will not be able to use USB ports to power most tubes. A simple test board provides the right bias and convenient way to connect the power supply. One power supply supplies power to the heater, while the other power supplies drive other voltages. A small DC-DC converter provides a high voltage b+ line from a 12V input.
Observing the operation of the pipe is certainly a way to test it. The days when tube testers were everywhere are long gone. But if you really need to test many tubes, you can still find some interesting ones in the second-hand market. If you are really motivated, you can even make your own pipes.