Testing a Tube without a Tube Tester

[M Caldeira] needed to test a tube and didn’t have a spare to do the old swap test. He also didn’t have a tube tester handy. Drawing inspiration from a 2015 video, he managed to cobble up an ad hoc tube tester using stuff around the workbench. You can see a video of the process below.

To duplicate his effort, you are going to need a few meters. Good thing they are relatively cheap these days. Usually, a tube tester has a way to adjust all the different parameters for the tube, but there’s no reason you can’t just set those parameters using your testbench power supplies.

Of course, that’s going to require high voltage power supplies. You won’t be able to use a USB port to power most tubes. A simple test board provides the right bias and convenient ways to connect the power supplies. One supply powers the heater, while other power supplies drive the other voltages. A small DC to DC converter provides the high voltage B+ line from  12V input.

Watching the tube in operation is certainly one way to test it. The days when tube testers were everywhere are long gone. But you can still find some interesting ones on the used market if you really need to test a lot of tubes. If you are really motivated, you can even make your own tubes.