My huge fluorescent/plasma "VU meter"...

[Externet]

How does it work ? How can I make others ?

I bought it about 7 years ago at a gadgets store, never found it advertised on the net, but also unsure on how to search for it. It is a 'novelty' type gadget; about 60 cm. long, 3 cm. diameter clear glass tube, has a built-in microphone and the driving electronics at one end of the 'fluorescent' ; powered with a 12VDC wall adapter.

The bright red plasma glow grows toward the end of the tube at the loudness of sound, it does not modulate its brightness, modulates its lenght.

Anyone knows anything about ?

Miguel

 

[Externet]

Pictures of the thingy attached...
Has no brand, no markings; I could reverse engineer the electronics, but don't know the 'gas discharge' tube principles.

A plain fluorescent tube; how could it be made to glow fed only from one end?

It may be something like this if not identical :
**broken link removed**

 

[Mikebits]

Based on the color, I would guess it is a helium or neon gas discharge tube.
Gas-discharge lamp - Wikipedia, the free encyclopedia

Here is a good description of how the tube might work.
Electric glow discharge - Wikipedia, the free encyclopedia

Quoted from source cited above:

The ions (which are positively charged) are driven towards the cathode by the electric potential, and the electrons are driven towards the anode by the same potential.

 

[Menticol]

No, it can't be a discharge tube Mike, because a discharge tube brights equally across its lenght and very intensely, so Externet would be blinded with fast tempo music.

Also the power consumption of a discharge tube is very high, much more than a wall adapter

I guess this thing is very similar to a "Magic Eye" tube, found in old tube radios to show signal strenght. I have one at my home!

**broken link removed**

 

[Externet]

Its transparent gas (when off) glows just as neon red like those in bar windows. The picture shows it lit to about 4/5 length for that particular instant of the picture. With varying audio, it changes length responding very fast.
The vacuum tube from Menticol is like a micro CRT oscilloscope, a phosphor wall and electron beams colliding on the back of the phosphor, No plasma/gas in that one.

Removing the end cap on my thingy, there is no electrode or wiring, just a piece of foam at the tip of a glass pipe to absorb shocks. The schematic also shows no connection.

Edited : added ---> neared my oscilloscope lead, shows 130KHz, 25Vp-p at 20cm from the tube.

 

[Menticol]

What about if the wiring is inside the glass tube?

Well, the Magiceye tube glows green, but I have found a thing called Tuneon, older than Magiceye, that glows red.

Can't you take all the system apart and put the pictures? It's risky, but it's for scientific purposes!

 

[Externet]

I prefer not to risk it, the housing is thermowelded, no screws to remove, no clips nor latches and cannot replace it if I break it as I do not know who sells it now.
And chances are there will be nothing surprising, just as the schematic shows.
There is no wires inside / outside the tube, checked with magnifying glass. Is is fully transparent.

Found something similar:
**broken link removed**
Miguel

 

[Menticol]

Deleted post, It wasn't neither a IN-13 Nixie Tube

 

[Mikebits]

No, it can't be a discharge tube Mike, because a discharge tube brights equally across its lenght and very intensely, so Externet would be blinded with fast tempo music.

Not quite acurate. A gas discharge tube just needs a high voltage potential. AC adapter to HV DC-DC converter would do the trick.
Since the Gas in the tube is charged and illuminates based on cathode to anode charge. One may be able to vary the charge based on HV modulation to the tube.

 

[unclejed613]

the high voltage (RF) is fed into the bottom of the tube. the bottom electrode is the only electrode in the tube. the varying length is caused by the variation of the space charge around the electrode.