THE GREAT MULLARD MAGIC BLOG — grid winding

As we have previously seen in this blog series, grids were produced in continuous  4 feet lengths and then cut to size for valve assembly - just like in the photo below: - As Mullard used millions of grids annually - all of which were cut by hand - in order to increase consitency and throughput, something had to be done.   Accordingly, the Mullard Engineering Department developed an automated grid cutting machine in which grid lengths are loaded into glass hopper tubes which allow whole strips to be cut to length sequentially.  All an operator needed to do was...

In the preceding two blog entries, I have discussed how tungsten wire was produced by Mullard's - incidentally, exactly the same process was used to make molybdenum wire too.   Both of these wire types were used to manufacture the grids we see in multi electrode cages.   As you can no doubt imagine, the performance of a valve is dependant upon extreme accuracy in the winding and positioning of these grids so let's have a look at what's involved in doing so. Let's consider the Mullard EF86, a B9A pentode used for many applications from TV IF strips to...

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...