When tubes were king, you could go to a drugstore with a box full of them from your TV. There would be a tester that would tell you what tubes were bad and, of course, you could buy the replacements for them. That kind of tube tester was pretty simple. If you wanted to really know how to design with a tube or test its parameters, you were much better off with a curve tracer like the Tektronix 570 that [tomtektest] shows off in two recent videos that you can see below.
That piece of kit fell into [Tom’s] lap thanks to an observant delivery driver. The 1955 instrument is very similar to a semiconductor curve tracer but, of course, has the ability to provide much higher voltage for the tubes. The basic idea is that the X axis sweeps from a few volts up to 100s of volts. The vertical scale will show the plate, screen, or grid current. From those curves you can learn a lot about the characteristics of the tube.
Accommodating the various tube pinouts takes a patch panel that would be at home on an old-style computer. You might wonder why you’d need all this data on a commercial tube. Like transistors, tubes had published data, but no two tubes would be exactly alike. It was very common in certain circuits to hand sort tubes of the same type to find tubes that closely matched.
[Tom] does a nice job of taking us through the device’s block diagram, shows us some of the schematic, and — of course — demonstrates the operation. He even shares some hacks to fix some oscillations in the tester’s circuits. While we don’t miss lugging those heavy beasts around, but somehow using an instrument with a screen that weighs more than 25 pounds makes you feel like you accomplished something.
If you want to build out your own tracer for solid-state instead of hollow state, it isn’t that expensive. Of course, one of these old 570s would be just the ticket if you were building your own tubes.