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.

4 thoughts on “Ask MAKE: Modding Vacuum Tubes with LEDs

  1. Some old tubes are still in pretty high demand in some circles. Others not so much. Very few models are being produced any more and probably none in quite the same glass envelope styles that they originally were. When you break them you take them out of circulation forever. If you have some tubes laying around that you would like to do this to it might be a nice thing to post around some antique radio or ham boat-anchor forums to make sure they aren’t rare ones somebody might need.

    If it turns out your junk is someone else’s treasure you could of course sell them or if you just want your LED lit tubes you might arrange to trade them for tubes that are already burnt out or maybe ones that are just too common to matter yet. You might make someone very happy.

  2. Yes, I have to agree with morgauxo’s comment. Don’t destroy tubes that are still good. They still command top dollar on eBay (if they’re) good and some of the audio ones are second to none sound wise (EL34, KT66, KT88, 6550, 6L6, 12AU7, 12AX7, 6SN7, etc…).

    I used to turn my nose up at tube stuff but now I have a pair of homemade 50 Watt RMS Class A/B mono-block amps and I just can’t listen to solid state amps anymore. The tubes just sound too sweet to my ears.

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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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