Introduction

Over the years I have come across different giant projects. There is a Giant Arduino Uno, a Giant LED, a Giant Resistor ohmmeter, a Giant NE555 footstool and lately a Giant SD card. I’m not sure why people think is so interesting to upscale tiny objects from around there lab, I guess there are different stories and reasons. But now there is also the Giant Vacuum Tube Lamp and here is my story about it.

Inspiration

The other evening I was trying to get an overview of all our digital images that were spread all over the digital place. From old smartphones including online backup services that were about to expire or filled up, like Dropbox, Google Drive and OneDrive to different folders in different computers and backup hard drives to an old camera in a drawer. On an old hard drive I found some very interesting images taken longtime ago at a music festival with the famous, now dead, Danish musician Kim Larsen that I have heard on the radio since my childhood. In the background of the stage stood four vacuum tube models the same height as a person. They looked rather realistic with orange light simulating the filament heater and blue light simulating the fluorescence that can be seen in some power tubes. My guess is that they should look like EL34 power tubes typically found in guitar tube amplifiers. I remember that I thought they looked so cool and wanted to build something similar. But I never got anything done about it – until now.

When I saw the images again I got the same excitement and started to search around for the part that would define the rest of the design – the glass envelope. I was surprised to find many different products available. Typically used as a glass bell for displaying flowers or other creative things as an interior decoration. Most of them had a dome shape at the end without a tip resembling the exhaust tip on a vacuum tube. This was not a big problem because it looked a lot like the EL34 where the exhaust tip is hidden at the bottom of the tube between the pins. The dimensions of the glass bell gave me some dimensions to continue my work with the search for the rest of the parts. An EL34 measures 33.3 mm in diameter and is 98 mm high including the socket but without the pins. The closest I could come to this relationship, using the largest glass bell I could find, was one that had a diameter of 21.5 cm and a height of 52.5 cm. This gives an upscaling factor around 7 for both diameter and height.

Design and construction

After settling on the outer dimensions I started to search for inspiration for the internal structure of the vacuum tube. I wanted it to look a bit more realistic than the ones I saw at the stage and another project I found online.

The outer structure of the tube is inspired by an EL34 tube mainly because the glass bell has a rounded top like an EL34 without an exhaust tip at the top. The connection pins on an EL34 is connected to a brown or black socket part that would be a perfect way to connect the glass bell with the connection pins on my model. 

The internal structure is inspired by the front cover of a book from my collection called Build Your Own Audio Valve Amplifiers. I didn’t want it to look like the internal of an EL34 because there isn’t much to see other than a big solid metal plate. I found an EF89 in my parts bin that has a nicer metal grid around the heater and grid wires that can be seen beneath. The EF89 is commonly used as a R.F. Pentode in AM/FM radios. 

Starting from the inside and out the heater is built from two 230V LED filament light bulbs mounted top to top. Around the bulbs an enameled copper wire is wrapped imitating a grid. Around this grid another grid is wrapped around two threaded rods. The last layer is a thin perforated metal plate imitating the outer metal plate. The six threaded rods are held together in each end by the insulating spacers made from laser cut acrylic plates that are sanded to give them a matt finish like mica. At the top end two of the threaded rods are extended to work as mounting for the getter ring. At the bottom the internal structure of the vacuum tube is connected to the socket by thin copper tubes going from the threaded rods down to the pins in the socket. To straighten the copper tube before bending to the right angles I used my Tube Straightening Tool.
The socket is made by laser cut plates of plywood glued together to give the right height. The plates were made with holes for the eight pins which are glued on. The curved surface of the socket has been sanded down and plastered before a spray primer has been applied. The last step was to paint it with a black glossy spray paint to make the surface look piano black.
The two light bulbs are connected in parallel and the power cables to them are routed through two of the copper pipes and down through two individual pins and connected to a transparent copper wire. 

Final details

There are still room for minor upgrades:

• Make larger cutouts in the pins where the power cables go through them.
• The getter ring should be sanded and painted silver to look like metal.
• The top part of the glass bell should be painted dark silver to look like vaporized barium.
• As a lamp the amount of light from the two light bulbs is perfect, but as a model of a vacuum tube it would be nice to add a light dimmer to make the filament look a bit more realistic.

Parts list

1x Glass bell – glass envelope
9x 12mm round plywood plates – socket
8x metal tubes – pins
6x M6 metal threaded rods with nuts – internal structure
2x acrylic plates – insulating plates
1x acrylic circle – getter ring
2x LED filament light bulbs – filament
8x copper tubes – connection between pins and internal structure
1x Enameled copper wire – grid
1x Thin perforated metal plate – outer plate
1x 230V transparent copper wire 
8x Acrylic plate for connecting pins and copper tube
4x Acrylic plate for light bulbs
1x Acrylic socket top plate

Specification

Final thoughts

I think my giant vacuum tube lamp turned out almost as I had hoped for when I imagined it in my head. I spend the most time on completing the socket because I wasn’t happy with the result after the first time I painted it. The surface wasn’t smooth enough, so I had to sand down the paint and primer to make the surface more even before repaint. This had been a much easier task if I had had the right tools like a belt or disk sander to sand the wood in the first place. Much of the design has also been work in progress while building it since I did not made a complete 3D drawing of the vacuum tube prior to the build. That made it necessary to adjust and modify some parts throughout the build.
I think the final result looks much like a real vacuum tube (except for the bright heater) and I’m especially happy with how the connections from the pins to the internal structure has been made with thin copper tubes that looks realistic.

If you have any feedback please comment below or contact me. If you are interested in buying your own giant vacuum tube lamp please contact me and convince me to make another one for you.

Indlægget Giant Vacuum Tube Lamp blev først udgivet på Daths Garage.