1:6 Scale Vacuum Tubes

One of the best features of 70s music is the warm tones produced by analog instruments and amplifiers. That warmth was made possible by the use of vacuum tubes.

When electrons flow through a vacuum, carrying “musically” charged samples from an instrument or a microphone, the amplified signal distorts in a way that is more pleasant to the human ear than via digital circuits. That is, the frequencies are handled more naturally in an analog circuit versus in a digital circuit where those frequency values are quantized at a certain interval, clipped (rounded) to the nearest numeric value, amplified, and then converted back into an analog signal that can actually move a speaker membrane. As much as digital technology has advanced since the 70s and 80s, a trained human ear can still tell the difference, and that difference boils down to two flavors of distortion: Warm & Cool

The back of a HIWATT CUSTOM 100 amplifier head.

A big challenge in reproducing such equipment in 1:6 scale is how to replicate those vacuum tubes visually. Not just to sit there, but to light up, glow and even breathe with the music.

So here’s my engineering solution:

EDGELEC 30pcs 12 Volt 5mm UV LED Lights Emitting Diodes Pre Wired 7.9 inch DC 12v Ultraviolet LED Light Clear Lens Small LED Lamps

I found these little glass test tubes (or vials) on Etsy. The glass part is 7.8mm OD, 5.2mm ID, and 32mm long. I had to order them from China. Ten for less than $20. Shipping take long long time.

Stren Original Monofilament Fishing Line

That’s less than $30 worth of parts. The idea is to mount the 5mm OD (outside diameter) LEDs wherever there’s a vacuum tube in the equipment. Now those LEDS are only 8.5mm tall, so that’s not tall enough for a typical vacuum tube. So, we’ll cut a piece of the clear rigid tubing to about 1 inch, and then fit it over the LED. That should work snugly because the ID (inside diameter) of this particular tubing is 5mm.

And the pièce de résistance is that we’ll cut some clear blue fluorescent monofilament (fishing line), fold it over a few times, and insert it into the clear tube. Then seal the top of the tube shut, or maybe plug it or cap it.

Now, when powered up, the UV light will illuminate the glow-in-the-dark fishing line and it should look just like a vacuum tube, also illuminating any neighboring photoreactive materials.