Learning About Vacuum Tubes?

Comments

• kf4ixm Posts: 529

  2010-04-05 22:42 edited 2010-04-05 22:42

  Check this video out...
  
  http://www.dailymotion.com/video/x3wrzo_fabrication-dune-lampe-triode_tech
• Kyle L. Posts: 21

  2010-04-05 22:59 edited 2010-04-05 22:59

  That's pretty cool, kf4ixm. Thanks!
• Phil Pilgrim (PhiPi) Posts: 23,514

  2010-04-06 00:13 edited 2010-04-06 00:13

  Go to your local library and see if they have an older copy of the Radio Amateur's Handbook. There should be plenty of info there to get you started.
  
  -Phil
• Erik Friesen Posts: 1,071

  2010-04-06 00:24 edited 2010-04-06 00:24

  teslapress.com/vactube.html
  
  There is an interesting article in nuts and volts (listed in the above link)
  
  It goes on to explain in some other articles in the same issue that vacuum tubes are still in use. They apparently are capable of very high amperage.
• localroger Posts: 3,452

  2010-04-06 00:30 edited 2010-04-06 00:30

  There is a book I learned tube electronics from which was in my high school library -- I have no idea the author or title, but it was published in the early 1940's. (And no, I'm not THAT old, I was in high school in the 1970's; semiconductors were all around but there were also still lots of tubes in circuits, particularly for power applications.) The book was fairly thick and arranged very sensibly, encouraging you to breadboard circuit modules (as in breadboard "on slabs of wood") which you could then arrange into various complete circuits as you got more proficient. I never did any of the projects but I loved the presentation, even though it was kind of hilarious that there was a chapter "proving" that television was impossible based on the sensitivity and frequency response of vacuum tube photodetectors that might be used in a scanning-disk system.
  
  The main thing with tubes is that they amplify NEGATIVE voltages. I've thought of trying to drive a magic eye (I own two in my tube collection) from the Prop, but I'd have to use a charge pump to generate up to -6VDC to do it.
• localroger Posts: 3,452

  2010-04-06 00:36 edited 2010-04-06 00:36

  HOLY CARP LOOK WHAT I FOUND: http://www.pmillett.com/tecnical_books_online.htm
• bill190 Posts: 769

  2010-04-06 03:04 edited 2010-04-06 03:04

  Vacuum fluorescent display (VFD)...
  ..."The principle of operation is identical to that of a vacuum tube triode"...
  http://en.wikipedia.org/wiki/Vacuum_fluorescent_display
  
  And you can buy one here...
  http://www.parallax.com/Store/Accessories/Displays/tabid/159/CategoryID/34/List/0/Level/a/ProductID/57/Default.aspx?SortField=ProductName%2cProductName
  ·
• Kyle L. Posts: 21

  2010-04-06 04:55 edited 2010-04-06 04:55

  That's great stuff, everyone. Thanks!
  
  That online book collection, localroger, looks fantastic! I actually bought a couple of those books, too. :P Thanks!
• erco Posts: 20,261

  2010-04-06 16:55 edited 2010-04-06 16:55

  Long before Forest Mimms' most excellent Engineers Notebooks, I got hooked on a hand-me-down copy of ·"Elements of Radio" in my formative years. A great beginner book from the 1950s, talks all about diodes, triodes, etc. Led directly to my Ham Radio license and trusty Heathkit vac-tube rx/tx/vfo. Long live the 0B1 voltage regulator! Worth having on your shelf.
  
  http://www.alibris.com/search/books/qwork/2001715/used/Elements%20of%20radio·has $5 copies.
  
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• HollyMinkowski Posts: 1,398

  2010-04-06 18:27 edited 2010-04-06 18:27

  Tubes are actually interesting....and they look like they would be very durable, as long as the filament lasts.
  I wonder if the basic properties of vacuum tubes were discovered by someone working on early light bulbs?
  
  You can picture some old guy building the base of an experimental bulb and he messes up the two wires
  holding the filament so he just sticks in some more and ends up with a bulb having both a hot filament
  and some extra wires. So he just experiments by hooking things up to one of the wires feeding the filament
  and one of the extra wires and discovers some odd effects
• Leon Posts: 7,620

  2010-04-06 19:11 edited 2010-04-06 19:11

  How about simulating some valve circuits using SPICE? You should be able to find some suitable SPICE models.
  
  The thermionic diode was invented by Edison, he added an electrode to a light bulb.
  
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  Leon Heller
  Amateur radio callsign: G1HSM
  
  Post Edited (Leon) : 4/6/2010 7:18:50 PM GMT
• erco Posts: 20,261

  2010-04-06 21:03 edited 2010-04-06 21:03

  Quite right, the "Edison Effect" was discovered accidentally when young Thomas was trying various means to reduce the gradual blackening inside light bulbs.
  
  Thermionic emission: http://en.wikipedia.org/wiki/Thermionic_emission
  
  
  
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• erco Posts: 20,261

  2010-04-06 21:24 edited 2010-04-06 21:24

  People under 40 won't remember helping Dad fix a vacuum-tube-based TV or radio. Any unit could have 3-12 "molto delicato" glass vacuum tubes; you had to remove them all, wrap each in kleenex, put 'em in a cigar box, and take them down to the drug store to test them manually yourself. Any one of the tubes could be bad. You tested each one individually on a big console with·umpteen·different sockets. You looked up the settings for each tube in a flip chart, manually adjusted several rotary switches and pots, plugged in one tube at a time, WAITED for the filament to warm up, pressed a test button, and read a neat old analog meter: GOOD, ???, BAD. New tubes went for for $2-5; then you rushed home and plugged 'em all back in, hopefully before 'Lost in Space' started! You just couldn't miss seeing wise-cracking robot B-9; there wouldn't be a Parallax robotics forum for another 40 years!
  
  Portable testers ·at http://www.vacuumtubes.com/hickok_752a.html·& ·http://tone-lizard.com/Tube_Testers.html
  
  
  
  
  
  
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  ·"If you build it, they will come."
• localroger Posts: 3,452

  2010-04-06 21:49 edited 2010-04-06 21:49

  Holly, tubes are the opposite of semiconductors in two important ways. They LAUGH at electrical insults that would destroy power electronics -- don't care about electrostatic discharge or overvoltages much at all, and I've seen transmitter finals abused so badly their plates were glowing cherry red which were fine once they were powered off and allowed to cool down. This was great for novice ham operators with random wire antennas because we could fire up our transmitters with a mismatch or forget and key the transmitter with the receiver switched in to the same antenna and it generally didn't damage anything. It was not unheard of to observe arcing between the internal components in very high voltage applications, and again have the tube remain undamaged by the abuse.
  
  But tubes only have a typical life of 5,000 hours (more was possible particularly for large expensive transmitter tubes, but this was a common design goal for small signal types); the filaments lose emissivity over time, and of course they can burn out. They're also mechanically fragile; the glass envelopes can break and the internal components can become dislodged or bent by shock forces. Depending on how the tube was sealed it could lose vacuum, either a little (becoming "gassy" which would alter their characteristics in all sorts of interesting, mostly bad ways) or outright failing. You could spot a glass tube that lost its vacuum because all tubes had a little spot of sprayed silver metal called the "getter," which was some very highly reactive metal meant to mop up stray gas molecules left in the envelope after sealing, and in a gassy tube the getter would turn white.
  
  Large tubes were so valuable there were actually shops capable of taking them apart, mechanically repairing them, and pumping down a new vacuum to put them back in service. This was a standard maintenance procedure for the large water-cooled tubes used to generate hundreds of thousands of watts, such as the finals of broadcast radio station transmitters.
• HollyMinkowski Posts: 1,398

  2010-04-06 22:17 edited 2010-04-06 22:17

  @localroger
  
  Did anyone ever make tubes with more than 1 filament?
  In case it burned out another could be switched in.
• Leon Posts: 7,620

  2010-04-06 22:56 edited 2010-04-06 22:56

  That was never done, AFAIK.
  
  Valves could be made very reliable by using less current through the heaters and low electrode voltages. The ones used in undersea telephone cable repeaters had a typical life of 100 million hours.
  
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  Leon Heller
  Amateur radio callsign: G1HSM
• localroger Posts: 3,452

  2010-04-07 00:08 edited 2010-04-07 00:08

  Actually, some of those big transmitting tubes did have multiple filaments as Holly suggested. This only works for medium wavelength direct filament triodes (like the finals or modulators for a class C AM radio transmitter) and lower frequencies because at higher freqs the tube geometry starts to become real important. (Actually, big transmitting tubes are a whole subject of their own, especially since they remain relevant for certain applications.)
  
  Something I wanted to mention before but forgot -- with direct filament tubes (where the filament is the cathode, not just a heater heating a tubular cathode) it was possible for vibrations of the filament wires to show up in the amplified output. This was especially noticeable in DC instrument amplifiers because you could pound the desk the amp was sitting on and make the output jump.
• Mike Green Posts: 23,101

  2010-04-07 00:28 edited 2010-04-07 00:28

  There have been several attempts at filament-less vacuum tubes. In one case, the thing was made of high temperature ceramics sintered together in layers with the cathode, grid, and plate materials and the whole thing was heated to red heat. The cathode was still coated with a phosphor-like material which would emit electrons when heated. More recently there have been devices with cathodes with arrays of hair-like tungsten electron emitters that would emit electrons just due to the electrostatic forces under bias and the geometry of the "hairs".
• localroger Posts: 3,452

  2010-04-07 01:08 edited 2010-04-07 01:08

  Yeah Mike, they keep trying to reinvent the electron tube
  
  Most people don't believe it, but even with the demise of the television CRT they probably still own a vacuum tube -- in their microwave oven. And kids, if you ever chance to throw out a microwave oven, DO NOT OMIT TO SALVAGE THE MAGNETS. Because microwave magnetron magnets are totally, awesomely cool.
• potatohead Posts: 10,261

  2010-04-07 04:02 edited 2010-04-07 04:02

  [noparse]:)[/noparse]
  
  This is a great thread. As a high schooler in the 80's, I ended up working with tubes a lot. I had a tube HAM rig (.5Kw, and yes, it would glow red on a mismatch) with xtal reference, tube Tek dual trace scope, used to repair several old TVs and Radios, including building a new power supply for an older Zenith tower, where the speaker utilized an active coil.
  
  There are many amplifier enthusiasts out there building guitar amps, to exploit the very properties localroger was talking about. Semi's just can't do a good riff the same way an over-driven tube can.
  
  The local market had a big, stand up tube tester, and I was given one very similar to the one shown, by the TV Repair tech, who learned of me, when I took a summer vacation and tuned enough neighborhood TV's to impact his business. [noparse]:)[/noparse] I would generate all the reference signals with a home computer, then work through the various stages of the TV, sorting out linearity, convergence, and overall color purity issues, finishing up with a reference adjustment to get "factory" color. He found out about this and put me to work on the bench for a coupla years... The real secret was the TV technology at the time wasn't capable of enough real fidelity to differentiate between a spot on pro adjustment, and one done by eye, a lens and a home computer, and would degrade over the course of a couple years, requiring frequent maintenance adjustment, which was the mainstay of the TV tech early on.
  
  If I it were me with that spark of interest today, I would deffo get some Nixies, a "magic eye" or two, and various vacuum phosphor displays. They look great, and actually do "warm up" too. If it were not for me seeing the insides of a TV actually do something, like glow, make heat, buzz, etc... I might not have sparked the interest in electronics that I did.
  
  Cool magnet source noted !
  
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• Cluso99 Posts: 18,071

  2010-04-07 07:42 edited 2010-04-07 07:42

  My lecturer told us that a vacuum tube was just FET with a pilot light. LOL. To some extent, they are similar. BTW that was in 1970 :-(
  
  I re-built taxi vacuum tube based transceivers, converting them to the amateur 2m & 6m bands. Used to blow my 30A protection fuse on my Volkswagen 6V battery regularly. I always carried a spare fully charged battery and required it often.
  
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