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Audio and Video Talk
Valves / Vacuum Tubes
The function of the electron tube (DISCUSSION)
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<blockquote data-quote="ludo" data-source="post: 37756" data-attributes="member: 691"><p>Not quite. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink ;)" loading="lazy" data-shortname=";)" /></p><p></p><p>Dew, this will possibly sort of work for some triodes, but not all. The grid is usually made a couple of volts more negative than the cathode in order to shut off conduction through the tube. As the grid becomes less negative with respect to the cathode (ie as the grid "moves to the positive side of things" while remaining negativecompared to the cathode), at some point, conduction begins. </p><p></p><p>There are tubes with which one can make the grid more positive than the cathode, but I believe those are a bit rare in audio. Mars and F_D and Ampdog probably know lists of those off by heart, but I hope they will agree that triode grids are usually at lower voltages than cathodes, at least in our dealings with them. </p><p></p><p>Ie, triodes are depletion devices. Ie they conduct like there's no tomorrow when grid voltage=cathode voltage and there is (+) voltage on the anode. </p><p></p><p>If the grid and cathode are at the same voltage, the grid provides no "shielding/blocking" between the cathode and anode. N channel JFets are similar.</p><p></p><p>No how does one make the grid more negative than the cathode when you have no negative supply rail? Or am I getting ahead of you...?</p></blockquote><p></p>
[QUOTE="ludo, post: 37756, member: 691"] Not quite. ;) Dew, this will possibly sort of work for some triodes, but not all. The grid is usually made a couple of volts more negative than the cathode in order to shut off conduction through the tube. As the grid becomes less negative with respect to the cathode (ie as the grid "moves to the positive side of things" while remaining negativecompared to the cathode), at some point, conduction begins. There are tubes with which one can make the grid more positive than the cathode, but I believe those are a bit rare in audio. Mars and F_D and Ampdog probably know lists of those off by heart, but I hope they will agree that triode grids are usually at lower voltages than cathodes, at least in our dealings with them. Ie, triodes are depletion devices. Ie they conduct like there's no tomorrow when grid voltage=cathode voltage and there is (+) voltage on the anode. If the grid and cathode are at the same voltage, the grid provides no "shielding/blocking" between the cathode and anode. N channel JFets are similar. No how does one make the grid more negative than the cathode when you have no negative supply rail? Or am I getting ahead of you...? [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
The function of the electron tube (DISCUSSION)
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