Remember the story of Wilhelm Röntgen discovering X-ray using vacuum tube? Much like the widespread use of x-ray, after the invention of the tube by Marconi, in the early twentieth century, the vacuum tube was an essential element in every electric element built to receive and transmit electric signals and data in the form of radio signals. A vacuum tube, as you may already know, is a near-vacuum electric tube that controls the flow of electricity in between its two electrodes.
In the vacuum tube, the filament attached to the cathode heats up when current flows through it. The heated up cathode then emits electron that runs straight to the anode due to the attraction of charges. Despite its being old fashioned these days, many hobbyists and enthusiasts still use vacuum tubes to conduct experiments with. But many a time, grids break down, the filament sags or burns. Hence comes the knowledge of how to test a vacuum tube without a tester, if you don’t own any. Or how to test a vacuum tube with a multimeter.
Firstly, in order to know to detect the problem, you’ll need to know the model of the tube and its specifications.Some models are best for cleaning stairs and some may be used to clean used to clean wet carpets wet carpets while others might be used in a generalized way. You need to know the construction procedure and the mechanics behind it to fully identify the problem with your tube. Has the glass envelope burst? Has one of the pins shorted out, and melted off? There might be a gas buildup in the gas envelope but the tube may still light up, although it won’t function. Or maybe, like all other products, your tube has worn off. The proper reason may only be revealed through proper knowledge of the ratings and pin diagram of your vacuum tube.
Go to the manufacturer’s site and download the specification of the tube. Once you know which pin is which, you’re ready to carry out the test.
The second thing you’ll need to test your tube is a multimeter, of course. If you have spare functioning tubes and a radio, you can also utilize those to test your vacuum tube.
The best tube tester is the socket or circuit for which it was intended. If your main circuit is working you can use it to test the tubes. Does the circuit function when the different tubes are put inside it? If your tube doesn’t power up the circuit, then it’s not functioning.
Another basic method is to measure the current using the multimeter (Ammeter in this case) when the heater is powered and a low voltage is applied between plate and cathode. Connect the positive of the multimeter to the cathode of the tube and the negative to the anode. Point the multimeter’s controlling needle to the Ampere section of the ring and notice if there is any current flow across the tube.
If you’re suspecting a filament burn, use your multimeter (ohmmeter in this case) to check between each two pins with a resistance between them. This is what drives a functioning filament. If there is no resistance between any two pins, the cause might be it’s a malfunctioning tube.
In short, the best way to test your tube is to study about it and know how it works. The more you know, the more likely you’ll find out about where to look despite the absence of a tube tester.