Ask MAKE: Modding Vacuum Tubes with LEDs

Bob asks:

I saw your article on the LED mod for old tubes. I have a box full and would like to do an array of tubes but I have no clue as to how to wire, power supplies etc. I can do the mechanical part. Could you help me as far the nitty gritty on making this project work?

I’m glad to hear you want to tackle the LED Vacuum Tube Mod, especially because you’d like to repurpose some hardware that you already have on hand.

Wiring LEDs is a great way to sharpen your electronics chops, and there are some great tools to help you in doing this. First you’ll need to decide how many LEDs you want to use in your display and how much voltage will be driving the LEDs. Since this is a relatively low-powered project, a 9 volt battery should be just fine for testing purposes.

LEDs usually come with a datasheet indicating their forward voltage and amperage. Take these and the numbers you just came up with and plug them into an online LED calculator such as this one. As an example, I chose 20 red LEDs for the array, with 9v as my driving voltage. The calculator gives a schematic for a 4 x 5 array of LEDs, which can light up five of your vacuum tubes with four LEDs each.

The calculator gives resistor values, so you’ll need to pick up some of those for yourself, and I suggest wiring up the circuit completely to make sure it works before stuffing them into the vacuum tubes. Make sure you observe polarity with the LEDs: the longer leg is positive, and the shorter one is negative.

If all is well, install them into the vacuum tubes and hook up a 9V wall wart power supply to your circuit. You can find one of these at your local electronics store. Just snip and strip the leads, insulate with electrical tape or wire shrink wrap, and make sure you use a multimeter to check polarity before completing this step.

Good luck with your project! If readers have additional notes to add, please do so in the comments section.


In addition to being an online editor for MAKE Magazine, Michael Colombo works in fabrication, electronics, sound design, music production and performance (Yes. All that.) In the past he has also been a childrens' educator and entertainer, and holds a Masters degree from NYU's Interactive Telecommunications Program.

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