Giant Electronic Vacuum Tube

Happiness is a warm...vacuum tube?

Harken back to the days of yesteryear, when people huddled around the old radio or black and white television for entertainment. Make a giant electronic vacuum tube(electron tube or valve) to bring back that warm glow and to remind us of the quality of sound that only an analog circuit can produce.

This is just a fun project to make giant things and to learn something along the way. It's also just a quick ible to get you to exercise your google-fu to look up new terms or vocabulary so all steps are sketchy. Start out with looking up the vacuum tube which is covered more extensively than I could ever do.

Another quick after dinner project from things gathered around the house...

Vacuum tubes come in various shapes but I had an empty spaghetti sauce glass jar and a taller plastic container. Their shapes are similar to the cylinders of vacuum tubes but only larger, hence the giant sized vacuum tubes.

I wanted to replicate that metallic coating that is present on the top inside of most vacuum tubes. I found out that is a coating done in manufacturing the tube. Usually made of Barium, it is heated and evaporated in a "getter" pan inside the tube under vacuum. It is flashed and condenses onto the inside of the glass tube. This is done so the Barium can interact with the impurities still left in the vacuum tube which can prevent the vacuum tube from working properly.

I used silver spray paint to "sputter" the inside of the containers. I used a piece of paper rolled up to mask the majority of the container and sprayed the paint through the open end. I think a second spray of black paint afterwards would darken and make the silver sputtering look more realistic. I used a really old can of silver spray paint that I did not thoroughly shake and mix so you see it was runny paint that came out first.

The base was constructed from cardboard scraps.

Cut out a few rounds of cardboard marked by tracing around the mouth of the container for size.

Wrap a strip around the bottom of the container to make a fitted collar.

Build up the inside of the base by gluing the rounds in place. You can use L shaped cardboard tabs to join the pieces. I stuffed in folded cardboard strips to bulk up the inside of the base. Cover over with the rounds. Papier mache to smooth out all the exposed cardboard edges.

I then used plastic straws for the vacuum tube pins. I glued in pieces of bamboo skewers to strengthen them up. You could also use cut dowels or your stash of collected IKEA pencils, actually, I was saving them to make a roulette wheel with the lazy susan...

I just did a quick lookup on the many different types of base pin configurations but what stuck in my mind was a 9 pin with one missing as the keyed base. I just divided the circle by eye and punched in holes with an awl. They needed to be enlarged with a screwdriver tip to fit the straw sections. They were then glued in and all trimmed evenly around.

This is where you integrate modern technology into your project. The magic here is using an Adafruit Circuit Playground microcontroller board. Since it has an onboard microphone and a ring of Neopixel LEDs, it is perfect for loading on a sound reactive sketch to have the lights flash to the varying sound volume.

I used the sketch from the Circuit Playground Seashell Pendant tutorial https://learn.adafruit.com/circuit-playground-seas...

Since this uses the FASTLED library for the Neopixels,

CHSV(map(i,0,NUM_LEDS-1,20,70), 255, 255); //constrained to yellow color, change CHSV values for rainbow

The function parameters can be changed 20,70 to 0,60 to give the red orange glow. You could also figure out which is the color range or Hue values for blue to get a cool blue glow. Fastled is based on the HSV color charting which is not the same as RGB commonly used.

The larger vacuum tube uses the same sketch but with an added neopixel strip. The same logic to light the onboard Neopixels was duplicated and scale changed to match the extended number of Neopixels on the strip.

I really only wanted to get the impression of the innards of a vacuum tube but it can be a complex mix of parts if it was accurately modeled. I don't know if there are any papercraft templates out there but real vacuum tube vertical pieces or plates fit into slots on the spacer rounds. The glowing heated filament center would be my Neopixel strip or the light from the Neopixels on the Circuit Playground board. I made a tube from plastic canvas to be the grid. I did not have any metal mesh to use and didn't want to do a wire winding around upright posts. Window screen material would have worked too. The grid gives a nice diffusion for the lights. The outer anode plates were pieces of stiff craft foam with similar cutouts.

The bases were painted with acrylic black. I think the original color might have been a really dark bakelite plastic brown though. The vacuum tube pins were covered with aluminum foil duct tape. You could also paint or use metallic rub-n-buff coatings. Develop your dry brush paint technique to get the look of metal. Also available are metallic paper tapes or metallic look adhesive vinyl shelf liner paper to cover.

One thing I did not get to was to put on some kind of marking on the tube. I suppose you could paint or use a metallic marker to designate what kind of vacuum tube you had made.

Once you have a giant vacuum tube, you should figure out what kind of mounting base it should have. Do you want it to be a one tube Marshall amplifier with the volume knob that goes to 11? You can make a bunch and install it in a nice retro McIntosh styled stereo amplifier base. Or just have it freestanding to look cool on your desk or as a nightlight on your bedstand.

Enjoy!