In previous blog entries we have seen how many individual valve components were made, now we will look at how they were assembled. For component manufacture, we also saw how many automated production machines were utilised, however, when we come to valve assembly, things were quite different in that manual dexterity utilising just hand tools and a few light jigs are essential - yes - your valve was truly 'hand made'.
Another difference is that component manufacture and the final stages of valve making - pumping, sealing and testing - were done at the two main Mullard factories at Blackburn and Mitcham, a large proportion of the assembly work was undertaken at a number of smaller 'feeder factories.' These feeder factories used small work groups to produce certain valve types with the record being held by the Gillingham feeder factory where 86 people produced 12500 miniature battery valves (D series) in a day with a rejection rate of just 60 - or 0.5%.
Let's now look at how this performance was achieved. We start with the individual components required being delivered to the feeder factories twice daily by a van which on it's return journey carried the assemblies prepared since it's prior visit. Each type of component was transported in a sealed metal container to prevent dust contamination.
From the transport containers all metallic components were fed into a muffle furnace where they were stoved under a hydrogen stream at 950oC for 10 minutes before being cooled for 20 minutes prior to issue to the valve assembly stations where runners filled the bench hoppers at the valve assembly stations: -
At these work stations, teams of girls worked to assemble the electrode cages of a particular valve type. A typical team comprised of one grid cutter, two assemblers and two welders. As you can see in the photo below, there were quite a few bits to put together for this DF91 RF pentode and unlike a typical chap assembler, when they had finished they didn't have any bits left over!!!!! : -