Author Topic: Terrible description of vacuum tubes.  (Read 825 times)

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Offline CirclotronTopic starter

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Terrible description of vacuum tubes.
« on: February 02, 2021, 04:58:56 am »
On the RS website I found this dreadful explanation of what vacuum tubes / valves are all about. For example:
Quote
Triode - Triode vacuum tubes have electric current flow generates a high potential from the anode to the cathode's ground potential.
https://au.rs-online.com/web/c/semiconductors/discrete-semiconductors/vacuum-tubes/
Dear oh dear...
 
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Offline helius

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Re: Terrible description of vacuum tubes.
« Reply #1 on: February 02, 2021, 06:35:08 am »
That reads like auto-translated gibberish.

Does RS actually sell tubes? They are made in small numbers but I am surprised that they would be stocked by any distributor.
They are not properly categorized as "semiconductors": the vacuum inside the glass is not a semiconductor, it has no band gap. These are vacuum-state devices similar in some ways to gas-state devices such as thyratrons, neon tubes, etc.
 

Offline T3sl4co1l

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Re: Terrible description of vacuum tubes.
« Reply #2 on: February 02, 2021, 07:21:54 am »
Honestly I'm more impressed that they went to the trouble of ordering them with house branding.


That reads like auto-translated gibberish.

Does RS actually sell tubes? They are made in small numbers but I am surprised that they would be stocked by any distributor.
They are not properly categorized as "semiconductors": the vacuum inside the glass is not a semiconductor, it has no band gap. These are vacuum-state devices similar in some ways to gas-state devices such as thyratrons, neon tubes, etc.

Or physically speaking, whereas a FET has charge carriers in the conduction or valence band (either side of the band gap), a vacuum tube merely promotes charge carriers further, into the free / unbound / vacuum state band.  The major operational differences are: ballistic transport (no ions to weigh* down the charge carriers), operation exclusively with electrons (you can't make holes in vacuum, not without them annihilating with regular electrons anyway -- or without using plasma physics to prepare naked, and far far heavier, protons), and much lower current densities due to the lack of charge balance, again due to the lack of ions.

(*Not just in terms of collision (friction, diffusion/drift transport), but literally, the effective mass of an electron is something like 100x higher in typical cases.  Crystals, being periodic structures, have an effect something like a waveguide, where the group and phase velocity can be all weird compared to the free particle case.  Ballistic transport is sometimes possible in semiconductors, for example GaAs has high enough... mobility, is it due to? -- where there's a small operating band above saturation velocity yet below avalanche (impact ionization) threshold.  Hence Gunn diodes, which are actually monodes -- a uniformly doped bar of semiconductor that sings when you make it sweat hard enough!)

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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