Wow. "Make your own vacuum tube"

This is pretty amazing:

Video on making a vacuum tube by hand.

(Lets see if Instructables likes Dailymotion videos...)

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Sorry, but what does a vacuum tube do?
It's like a ghetto amp/transistor
westfw (author)  Sandisk1duo8 years ago
It's a STEAMPUNK transistor! A heated filament (cathode) emits electrons that travel through vacuum to the anode. By putting assorted "grid" electrodes in between at various voltage, the amount of current that flows can be controlled. Naturally, the voltages involved are quite high, and the current used just to heat the filament is substantial. Aside from that, a vacuum tube behaves pretty-much like a field-effect transistor. The last surviving member of the vacuum tube family in common use is the CRT Tv-screen, where the anode is covered with phosphor, and some of the additional control signals managed to make the electrons travel in a tiny beam that is swept across the screen in a raster pattern to make pictures.
They are pretty inefficient.. but they can carry higher amperage... right?
westfw (author)  Sandisk1duo8 years ago
Some of the remaining applications for vacuum-tube like devices involve very high current, voltage, and power (eg, the magnetron that produces the microwaves in your oven is a kind of vacuum tube), but I don't think that it's fair to say that a generic vacuum tube is a higher amperage device than a generic solid state device. One of the factors that comes into play that it is relative easy to scale UP a vacuum tube compared to a semiconductor junctions (which is sort of inherently a nanoscale device.)
Am I getting this right?:
besides the heater element , there are 3 other components: grid, cathode and anode
the grid = input , low voltage
anode and cathode are on a high voltage powersupply(around 200-400v) , the speaker sits between the anode(or cathode?) and the tube , but since it works with such a high voltage , a transformer must be placed between the output of the tuba and the speaker, so a lower voltage reaches the speaker...
something like that?
Just started getting interested in vacuum tubes and i'm trying to make a simple 5 watt amplifier , but i need to know how they work first...
Yes, that's about right. You have all the complications of more modern circuits as well; high power amplifiers tend to be "push/pull" configurations, for example.
tiggerbob7 years ago
First of all, vacuum tubes were the predesessors to the transisters and were in common use until the late 1960's. I can remember, as a child, observing the glow of vacuum tubes in the back of my dad's stereo. Until the invention of the field effect transistors(FET), the vacuum tube was the only high input impedience(resistance) amplifier. Vacuum tubes were also capable of handling high currents which would have fried the early transistors. As a side note, the first electronic digital computer was built from vacuum tubes, filled an entire room and weighed several tons! Thank goodness for integrated circuits! For the most part, vacuum tubes faded from sight. Gone are the drug store tube testers. However, they are still used in some high-end audio synthesizers and amplifiers. Most of your large (not practice-sized) guitar amplifiers use vacuum tubes. Vacuum tube synthesizers are prized by digital composers add a degree of warmth and pleasant distortion to the sound.
Speaking of Vacuum tube computers, in 1951, Popular Science magazine said that someday, computers may actually weigh less than 1.5 tons (at the time it was ridiculed).
Sandisk1duo8 years ago
I'd rather buy one...
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