THE GREAT MULLARD MAGIC BLOG — control grid

Let's continue this story by today looking at GRIDS.  These are found between cathode and anode except for diodes which have just two electrodes - the anode and cathode.  The purpose of a GRID is to control the value of anode current.  In triodes, we have just one GRID - the control grid.  In pentodes we have three grids with the inner one being the CONTROL GRID, the next the SCREEN GRID and the outer one the SUPPRESSOR GRID.   In each case, the GRID is a cylindrical or ellipsoid spiral of fine molybdenum or molybdenum alloy wire wound onto...

Continuing our journey to look at what's inside a valve, today we are going to look a little further at our EL37 pentode with the envelope broken open.  After a little more surgery on the ELECTRODE CAGE we can see in the centre. the white vertical cylinder of the CATHODE, surrounding that are the three concentric grids, the inner being the CONTROL GRID, then comes the SCREN GRID and finally the SUPRESSOR GRID.