Partial internal structure of a type 6П1П (English:6P1P) miniature 9-pin beam tetrode vacuum tube manufactured in the former Soviet Union circa 1980s. In this view, the envelope and anode have been removed. The two tall sheet metal electrodes to the left and right are the beam confining or beam forming plates. The beam forming plates limit the included angle of the beams and prevent anode secondary emission electrons outside of the beam region from going to the screen grid.
<a href="//commons.wikimedia.org/wiki/User:Mister_rf" title="User:Mister rf">Mister rf</a>
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<span class="int-own-work" lang="en">Own work</span>