A Pentode

a <a href="https://en.m.wiktionary.org/wiki/thermionic_valve" title="thermionic valve" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">thermionic valve</a> similar to a <a href="https://en.m.wiktionary.org/wiki/tetrode" title="tetrode" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">tetrode</a> with the <a href="https://en.m.wiktionary.org/wiki/addition" title="addition" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">addition</a> of a third grid, the <a href="https://en.m.wiktionary.org/w/index.php?title=suppressor_grid&action=edit&redlink=1" class="new" title="suppressor grid (page does not exist)" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(221, 51, 51); hyphens: none;">suppressor grid</a>; was/is used in high <a href="https://en.m.wiktionary.org/wiki/quality" title="quality" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">quality</a> <a href="https://en.m.wiktionary.org/wiki/audio" title="audio" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">audio</a> and <a href="https://en.m.wiktionary.org/wiki/radio" title="radio" style="background: none rgb(255, 255, 255); margin: 0px; padding: 0px; border: 0px; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-stretch: inherit; line-height: inherit; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Lato, Helvetica, Arial, sans-serif; vertical-align: baseline; color: rgb(107, 75, 161); hyphens: none;">radio</a> products