Tungsten cathodes

Post #48,090 by Andrew Grygus 8/4/02 11:52:55 PM 8/4/02 11:57:35 PM Reply	Tungsten cathodes - not - Tungsten is used for the filament, but raw filament cathodes went out around the time Edison died. Recent cathodes have a tungsten filament folded up inside a metal sleve (filament is coated with an insulating material so the folds don't short out). The metal sleve is coated with a rare earth material that is a much better emitter of electrons than tungsten. Unfortunately, this coating will eventually become poisoned by stuff that evaporates off the internal components of the CRT. Back in the '50s, when TV tubes were really expensive, there were "do or die" devices that would overvoltage the filament, hopefully not enough to blow it, but enough to boil the contaminents off the sleve. Color tubes don't seem to burn images like monos did, thought the phosphor may degrade with time, so screen savers have been primarily entertainment in recent years. Disclaimer: I am not an expert in cathode ray tubes, but having been involved with vacuum tubes since well before the CK722, and a [link\|http://www.geekculture.com/geekculturestore/webstore/tubesrock.html\|vacuum tube enthousiast] to the present day, and having had a father who worked as a process engineer (now known as a "manufacturing engineer") for Tung-Sol when it was a major manufacturer of vacuum tubes, I am not entirely unaware of issues involving cathodes (or anodes, for that matter). ------- PS I own one of those big 4-pin carbon anode transmitting triodes just like on the Ts (see link). It's about 8" high. [link\|http://www.aaxnet.com\|AAx] Edited by Andrew Grygus Aug. 4, 2002, 11:57:35 PM EDT Tungsten cathodes - not - Tungsten is used for the filament, but raw filament cathodes went out around the time Edison died. Recent cathodes have a tungsten filament folded up inside a metal sleve (filament is coated with an insulating material so the folds don't short out). The metal sleve is coated with a rare earth material that is a much better emitter of electrons than tungsten. Unfortunately, this coating will eventually become poisoned by stuff that evaporates off the internal components of the CRT. Back in the '50s, when TV tubes were really expensive, there were "do or die" devices that would overvoltage the filament, hopefully not enough to blow it, but enough to boil the contaminents off the sleve. Color tubes don't seem to burn images like monos did, thought the phosphor may degrade with time, so screen savers have been primarily entertainment in recent years. Disclaimer: I am not an expert in cathode ray tubes, but having been involved with vacuum tubes since well before the CK722, and a vacuum tube enthousiast to the present day, and having had a father who worked as a process engineer (now known as a "manufacturing engineer") for Tung-Sol when it was a major manufacturer of vacuum tubes, I am not entirely unaware of issues involving cathodes (or anodes, for that matter). AAx Collapse All History
Post #48,091 by Another Scott 8/5/02 12:04:49 AM Reply	You're right, of course. :-) Thanks.
Post #48,107 by Ashton 8/5/02 7:30:28 AM Reply	Can ya ID the T-shirt tube? Ancient - 4 pin. Rectifier is about all ya can do with 2 left after fil. It's before my time, tho I've seen most.. back to the De Forest Audion. The demise of Heathkit and the other kit suppliers seemed to parallel the rise of dumbth - as well as cheap disposable electronics. Fewer and fewer it seems, are much interested in really understanding how things work. As teaching tools (while scoring a decent stereo in the process) - I think the logic of tubes was much easier to grok than 'holes' and current-controlled devices - as all semis are. Also bulletproof. (If occasionally lethal to the terminally sloppy with sweaty palms). Anyway.. I think even the music was psych. enhanced in a dim living room - with two pair of KT-88s (and bright rectifier in background) epitomizing POWER you can See! Still have a box of (small signal) new tubes in garage.. Russia seems to be the new tube superpower (!). Early Tek portables had/have some tiny glass HV rectifiers and.. nuvistors! for the pre-FET input amps.. Now Those were cute! itty bitty ceramic tubes the size of a large xsistor - triodes thru pentodes. {sigh} I resisted picking up a Keithly tube (+chopper) picoammeter on eBay.. You can do femtoamps with a National Semi op-amp now - in fact Bob Pease scratched out a circuit whereby you can notice a change of ~10 more/less electrons! Eerie almost. Tubes \ufffdber Alles
Post #48,143 by Andrew Grygus 8/5/02 11:26:25 AM Reply	It's an Amperex 211D It turns out I have two of them. It's a a high power transmitting triode. One of the two heater pins is also the cathode pin (heater floats at cathode voltage). That leaves one pin for plate and one pin for control grid. Anode is sintered carbon because metal would buckle at the temperture these things ran at. Hight 7-1/2", dameter 2-1/4" [link\|http://www.aaxnet.com\|AAx]
Post #48,262 by a6l6e6x 8/5/02 8:53:44 PM Reply	The last glowing anode I saw was in the early 1960's,... a ham friend of mine built a transmitter from scratch. In the garage I have a Sylvania 23Z9, (I just checked) so I have a private mini-museum too! It's a Compactron, from the dying days of tubes. Alex "Television: chewing gum for the eyes." -- Frank Lloyd Wright

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