SherbyNet - /page/wikibook/entry.mu

Micron Document

<!DOCTYPE html>

<title>Control grid</title>

</head>

<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Control grid</span></span>

</h1>

</header>

<p>The <b>control grid</b> is an <a href="Electrode" title="Electrode">electrode</a> used in amplifying <a href="Vacuum_tube" title="Vacuum tube">thermionic valves</a> (vacuum tubes) such as the <a href="Triode" title="Triode">triode</a>, <a href="Tetrode" title="Tetrode">tetrode</a> and <a href="Pentode" title="Pentode">pentode</a>, used to control the flow of electrons from the <a href="Cathode" title="Cathode">cathode</a> to the <a href="Plate_electrode" title="Plate electrode">anode</a> (plate) electrode. The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by the anode. The control grid was invented by <a href="Lee_De_Forest" class="mw-redirect" title="Lee De Forest">Lee De Forest</a>, who in 1906 added a grid to the <a href="Fleming_valve" title="Fleming valve">Fleming valve</a> (<a href="Thermionic_diode" class="mw-redirect" title="Thermionic diode">thermionic diode</a>) to create the first <a href="Amplifier" title="Amplifier">amplifying</a> vacuum tube, the <a href="Audion" title="Audion">Audion</a> (<a href="Triode" title="Triode">triode</a>).

</p>

<div class="mw-heading mw-heading2"><h2 id="Operation">Operation</h2></div>

<p>In a valve, the hot cathode emits negatively charged <a href="Electron" title="Electron">electrons</a>, which are attracted to and captured by the anode, which is given a positive voltage by a power supply. The control grid between the cathode and anode functions as a "gate" to control the current of electrons reaching the anode. A more negative voltage on the grid will repel the electrons back toward the cathode so fewer get through to the anode. A less negative, or positive, voltage on the grid will allow more electrons through, increasing the anode current. A given change in grid voltage causes a proportional change in plate current, so if a time-varying voltage is applied to the grid, the plate current waveform will be a copy of the applied grid voltage.

</p><p>A relatively small variation in voltage on the control grid causes a significantly large variation in anode current. The presence of a resistor in the anode circuit causes a large variation in voltage to appear at the anode. The variation in anode voltage can be much larger than the variation in grid voltage which caused it, and thus the tube can amplify, functioning as an <a href="Amplifier" title="Amplifier">amplifier</a>.

</p>

<div class="mw-heading mw-heading2"><h2 id="Construction">Construction</h2></div>

<p>The grid in the first triode valve consisted of a zig-zag piece of wire placed between the filament and the anode. This quickly evolved into a helix or cylindrical screen of fine wire placed between a single strand filament (or later, a cylindrical cathode) and a cylindrical anode. The grid is usually made of a very thin wire that can resist high temperatures and is not prone to emitting electrons itself. <a href="Molybdenum" title="Molybdenum">Molybdenum</a> <a href="Alloy" title="Alloy">alloy</a> with a <a href="Gold" title="Gold">gold</a> plating is frequently used. It is wound on soft <a href="Copper" title="Copper">copper</a> sideposts, which are swaged over the grid windings to hold them in place. A 1950s variation is the frame grid, which winds very fine wire onto a rigid stamped metal frame. This allows the holding of very close tolerances, so the grid can be placed closer to the filament (or cathode).

</p>

<div class="mw-heading mw-heading2"><h2 id="Effects_of_grid_position">Effects of grid position</h2></div>

<p>By placing the control grid closer to the filament/cathode relative to the anode, a greater <a href="Amplifier" title="Amplifier">amplification</a> results. This degree of amplification is referred to in valve data sheets as the <a href="Amplification_factor" title="Amplification factor">amplification factor</a>, or "mu". It also results in higher <a href="Transconductance" title="Transconductance">transconductance</a>, which is a measure of the anode current change versus grid voltage change. The <a href="Noise_figure" title="Noise figure">noise figure</a> of a valve is inversely proportional to its transconductance; higher transconductance generally means lower noise figure. Lower noise can be very important when designing a radio or television receiver.

</p>

<div class="mw-heading mw-heading2"><h2 id="Multiple_control_grids">Multiple control grids</h2></div>

<p>A valve can contain more than one control grid. The <a href="Hexode" class="mw-redirect" title="Hexode">hexode</a> contains two such grids, one for a received signal and one for the signal from a local oscillator. The valve's inherent non-linearity causes not only both original signals to appear in the anode circuit, but also the sum and difference of those signals. This can be exploited as a frequency-changer in <a href="Superheterodyne" class="mw-redirect" title="Superheterodyne">superheterodyne</a> receivers.

</p>

<div class="mw-heading mw-heading2"><h2 id="Grid_variations">Grid variations</h2></div>

<p>A variation of the control grid is to produce the helix with a variable pitch. This gives the resultant valve a distinct non-linear characteristic.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> This is often exploited in R.F. amplifiers where an alteration of the <a href="Grid_bias" class="mw-redirect" title="Grid bias">grid bias</a> changes the mutual conductance and hence the gain of the device. This variation usually appears in the <a href="Pentode" title="Pentode">pentode</a> form of the valve, where it is then called a variable-mu pentode or remote-cutoff pentode.

</p><p>One of the principal limitations of the triode valve is that there is considerable capacitance between the grid and the anode (C<sub>ag</sub>). A phenomenon known as the <a href="Miller_Effect" class="mw-redirect" title="Miller Effect">Miller Effect</a> causes the input capacitance of an amplifier to be the product of C<sub>ag</sub> and amplification factor of the valve. This, and the instability of an amplifier with tuned input and output when C<sub>ag</sub> is large can severely limit the upper operating frequency. These effects can be overcome by the addition of a <a href="Screen_grid" class="mw-redirect" title="Screen grid">screen grid</a>, however in the later years of the tube era, constructional techniques were developed that rendered this 'parasitic capacitance' so low that triodes operating in the upper <a href="Very_high_frequency" title="Very high frequency">very high frequency</a> (VHF) bands became possible. The <a href="Mullard" title="Mullard">Mullard</a> EC91 operated at up to 250 MHz. The anode-grid capacitance of the EC91 is quoted in manufacturer's literature as 2.5 pF, which is higher than many other triodes of the era, while many triodes of the 1920s had figures which are strictly comparable, so there was no advance in this area. However, early screen-grid tetrodes of the 1920s, have C<sub>ag</sub> of only 1 or 2 fF, around a thousand times less. 'Modern' pentodes have comparable values of C<sub>ag</sub>. Triodes were used in VHF amplifiers in 'grounded-grid' configuration, a circuit arrangement which prevents Miller feedback.

</p>

/* start https://en.wikipedia.org/ */

.mw-parser-output .portalbox{padding:0;margin:0.5em 0;display:table;box-sizing:border-box;max-width:175px;list-style:none}.mw-parser-output .portalborder{border:1px solid var(--border-color-base,#a2a9b1);padding:0.1em;background:var(--background-color-neutral-subtle,#f8f9fa)}.mw-parser-output .portalbox-entry{display:table-row;font-size:85%;line-height:110%;height:1.9em;font-style:italic;font-weight:bold}.mw-parser-output .portalbox-image{display:table-cell;padding:0.2em;vertical-align:middle;text-align:center}.mw-parser-output .portalbox-link{display:table-cell;padding:0.2em 0.2em 0.2em 0.3em;vertical-align:middle}@media(min-width:720px){.mw-parser-output .portalleft{margin:0.5em 1em 0.5em 0}.mw-parser-output .portalright{clear:right;float:right;margin:0.5em 0 0.5em 1em}}

/* end https://en.wikipedia.org/ */

</style>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

/* end https://en.wikipedia.org/ */

</style><div class="reflist">

<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.tpub.com/content/neets/14178/css/14178_74.htm">Variable mu valves</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20070310142129/http://www.tpub.com/content/neets/14178/css/14178_74.htm">Archived</a> 2007-03-10 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a></span>

</li>

</ol></div></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist li{margin:0;display:inline}.mw-parser-output .hlist.inline,.mw-parser-output .hlist.inline dl,.mw-parser-output .hlist.inline ol,.mw-parser-output .hlist.inline ul,.mw-parser-output .hlist dl dl,.mw-parser-output .hlist dl ol,.mw-parser-output .hlist dl ul,.mw-parser-output .hlist ol dl,.mw-parser-output .hlist ol ol,.mw-parser-output .hlist ol ul,.mw-parser-output .hlist ul dl,.mw-parser-output .hlist ul ol,.mw-parser-output .hlist ul ul{display:inline}.mw-parser-output .hlist .mw-empty-li{display:none}.mw-parser-output .hlist dt::after{content:": "}.mw-parser-output .hlist dd::after,.mw-parser-output .hlist li::after{content:" · ";font-weight:bold}.mw-parser-output .hlist dd:last-child::after,.mw-parser-output .hlist dt:last-child::after,.mw-parser-output .hlist li:last-child::after{content:none}.mw-parser-output .hlist dd dd:first-child::before,.mw-parser-output .hlist dd dt:first-child::before,.mw-parser-output .hlist dd li:first-child::before,.mw-parser-output .hlist dt dd:first-child::before,.mw-parser-output .hlist dt dt:first-child::before,.mw-parser-output .hlist dt li:first-child::before,.mw-parser-output .hlist li dd:first-child::before,.mw-parser-output .hlist li dt:first-child::before,.mw-parser-output .hlist li li:first-child::before{content:" (";font-weight:normal}.mw-parser-output .hlist dd dd:last-child::after,.mw-parser-output .hlist dd dt:last-child::after,.mw-parser-output .hlist dd li:last-child::after,.mw-parser-output .hlist dt dd:last-child::after,.mw-parser-output .hlist dt dt:last-child::after,.mw-parser-output .hlist dt li:last-child::after,.mw-parser-output .hlist li dd:last-child::after,.mw-parser-output .hlist li dt:last-child::after,.mw-parser-output .hlist li li:last-child::after{content:")";font-weight:normal}.mw-parser-output .hlist ol{counter-reset:listitem}.mw-parser-output .hlist ol>li{counter-increment:listitem}.mw-parser-output .hlist ol>li::before{content:" "counter(listitem)"\a0 "}.mw-parser-output .hlist dd ol>li:first-child::before,.mw-parser-output .hlist dt ol>li:first-child::before,.mw-parser-output .hlist li ol>li:first-child::before{content:" ("counter(listitem)"\a0 "}

/* end https://en.wikipedia.org/ */

</style><style data-mw-deduplicate="TemplateStyles:r1236075235">

/* start https://en.wikipedia.org/ */

.mw-parser-output .navbox{box-sizing:border-box;border:1px solid #a2a9b1;width:100%;clear:both;font-size:88%;text-align:center;padding:1px;margin:1em auto 0}.mw-parser-output .navbox .navbox{margin-top:0}.mw-parser-output .navbox+.navbox,.mw-parser-output .navbox+.navbox-styles+.navbox{margin-top:-1px}.mw-parser-output .navbox-inner,.mw-parser-output .navbox-subgroup{width:100%}.mw-parser-output .navbox-group,.mw-parser-output .navbox-title,.mw-parser-output .navbox-abovebelow{padding:0.25em 1em;line-height:1.5em;text-align:center}.mw-parser-output .navbox-group{white-space:nowrap;text-align:right}.mw-parser-output .navbox,.mw-parser-output .navbox-subgroup{background-color:#fdfdfd}.mw-parser-output .navbox-list{line-height:1.5em;border-color:#fdfdfd}.mw-parser-output .navbox-list-with-group{text-align:left;border-left-width:2px;border-left-style:solid}.mw-parser-output tr+tr>.navbox-abovebelow,.mw-parser-output tr+tr>.navbox-group,.mw-parser-output tr+tr>.navbox-image,.mw-parser-output tr+tr>.navbox-list{border-top:2px solid #fdfdfd}.mw-parser-output .navbox-title{background-color:#ccf}.mw-parser-output .navbox-abovebelow,.mw-parser-output .navbox-group,.mw-parser-output .navbox-subgroup .navbox-title{background-color:#ddf}.mw-parser-output .navbox-subgroup .navbox-group,.mw-parser-output .navbox-subgroup .navbox-abovebelow{background-color:#e6e6ff}.mw-parser-output .navbox-even{background-color:#f7f7f7}.mw-parser-output .navbox-odd{background-color:transparent}.mw-parser-output .navbox .hlist td dl,.mw-parser-output .navbox .hlist td ol,.mw-parser-output .navbox .hlist td ul,.mw-parser-output .navbox td.hlist dl,.mw-parser-output .navbox td.hlist ol,.mw-parser-output .navbox td.hlist ul{padding:0.125em 0}.mw-parser-output .navbox .navbar{display:block;font-size:100%}.mw-parser-output .navbox-title .navbar{float:left;text-align:left;margin-right:0.5em}body.skin--responsive .mw-parser-output .navbox-image img{max-width:none!important}@media print{body.ns-0 .mw-parser-output .navbox{display:none!important}}

/* end https://en.wikipedia.org/ */

</style></div><div role="navigation" class="navbox" aria-labelledby="Thermionic_valves110" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><style data-mw-deduplicate="TemplateStyles:r1239400231">

/* start https://en.wikipedia.org/ */

.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}

/* end https://en.wikipedia.org/ */

</style><div id="Thermionic_valves110" style="font-size:114%;margin:0 4em"><a href="Vacuum_tube" title="Vacuum tube">Thermionic valves</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%">Theoretical principles</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Thermionic_emission" title="Thermionic emission">Thermionic emission</a></li>

<li><a href="Work_function" title="Work function">Work function</a></li>

<li><a href="Hot_cathode" title="Hot cathode">Hot cathode</a></li>

<li><a href="Space_charge" title="Space charge">Space charge</a></li>

<li><a href="Suppressor_grid" title="Suppressor grid">Suppressor grid</a></li>

<li><a href="Plate_electrode" title="Plate electrode">Anode</a></li>

<li>Glowing anode</li>

<li><a href="Getter" title="Getter">Getter</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="List_of_vacuum_tubes" title="List of vacuum tubes">Types</a></th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Vacuum_tube#Diodes" title="Vacuum tube">Diode</a></li>

<li><a href="Audion" title="Audion">Audion</a></li>

<li><a href="Triode" title="Triode">Triode</a></li>

<li><a href="Acorn_tube" title="Acorn tube">Acorn tube</a></li>

<li><a href="Nuvistor" title="Nuvistor">Nuvistor</a></li>

<li><a href="Tetrode" title="Tetrode">Tetrode</a></li>

<li><a href="Beam_tetrode" title="Beam tetrode">Beam tetrode</a></li>

<li><a href="Pentode" title="Pentode">Pentode</a></li>

<li><a href="Pentagrid_converter" title="Pentagrid converter">Pentagrid</a> (Hexode, Heptode, Octode)</li>

<li><a href="Nonode" title="Nonode">Nonode</a></li>

<li><a href="Cathode-ray_tube" title="Cathode-ray tube">Cathode-ray tube</a></li>

<li><a href="Additron_tube" title="Additron tube">Additron</a></li>

<li><a href="Backward-wave_oscillator" title="Backward-wave oscillator">Backward-wave oscillator</a></li>

<li><a href="Beam_deflection_tube" title="Beam deflection tube">Beam deflection tube</a></li>

<li><a href="Charactron" title="Charactron">Charactron</a></li>

<li><a href="Compactron" title="Compactron">Compactron</a></li>

<li><a href="Eidophor" title="Eidophor">Eidophor</a></li>

<li><a href="Iconoscope" title="Iconoscope">Iconoscope</a></li>

<li><a href="Inductive_output_tube" title="Inductive output tube">Inductive output tube</a></li>

<li><a href="Kinescope" title="Kinescope">Kinescope</a></li>

<li><a href="Klystron" title="Klystron">Klystron</a></li>

<li><a href="Magic_eye_tube" title="Magic eye tube">Magic eye</a></li>

<li><a href="Cavity_magnetron" title="Cavity magnetron">Magnetron</a></li>

<li><a href="Monoscope" title="Monoscope">Monoscope</a></li>

<li><a href="Phototube" title="Phototube">Phototube</a></li>

<li><a href="Photomultiplier_tube" title="Photomultiplier tube">Photomultiplier</a></li>

<li><a href="Selectron_tube" title="Selectron tube">Selectron tube</a></li>

<li><a href="Storage_tube" title="Storage tube">Storage tube</a></li>

<li><a href="Sutton_tube" title="Sutton tube">Sutton tube</a></li>

<li><a href="Talaria_projector" title="Talaria projector">Talaria projector</a></li>

<li><a href="Traveling-wave_tube" title="Traveling-wave tube">Traveling-wave tube</a></li>

<li><a href="Trochotron" class="mw-redirect" title="Trochotron">Trochotron</a></li>

<li><a href="Video_camera_tube" title="Video camera tube">Video camera tube</a></li>

<li><a href="Williams_tube" title="Williams tube">Williams tube</a></li>

<li><a href="Fleming_valve" title="Fleming valve">Fleming valve</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Numbering systems</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li><a href="RETMA_tube_designation" title="RETMA tube designation">RETMA</a></li>

<li><a href="Marconi-Osram_tube_designation" class="mw-redirect" title="Marconi-Osram tube designation">Marconi-Osram</a></li>

<li><a href="Mullard%E2%80%93Philips_tube_designation" title="Mullard–Philips tube designation">Mullard–Philips</a></li>

<li><a href="Russian_tube_designations" title="Russian tube designations">Russian</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%">Examples</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="List_of_vacuum_tubes" title="List of vacuum tubes">List of vacuum tubes</a></li>

<li><a href="Tube_socket" title="Tube socket">List of tube sockets</a></li></ul>

</div></td></tr></tbody></table></div></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2023-01-11" href="https://en.wikipedia.org/wiki/?title=Control_grid&oldid=1133004402">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

</div>

</div></div>

</div>

</main>

</div>

</body></html>