THE GREAT MULLARD MAGIC BLOG — mullard

Electrode assemblies returned from feeder to parent factory were complete except for the getter and in the case of battery valves, the filament.  In both cases, these components were added at the parent factory, immediately prior to the assemblies being sealed into the envelope and the valve being pumped.   This was to avoid contamination of these labile components which were vacuum stored until useage. Attachment of the getter is a simple process where a strip of metal ribbon coated with getter material is welded to the stirrup wire at the top of the electrode assembly.    Insertion of the...

Today's Mullard archive photograph shows a Mullard Whyteleafe Valve Assembly Department operator removing an electrode cage from one of the dustproof boxes in which valve components were stored when not undergoing manufacturing operations.  As you can see, the operator's right hand holds a pair of welding tweezers with which she is about to weld a getter bar onto a selected electrode cage.  The BBC European Service Science Correspondent in 1953 was CL Boltz and he had much to say about the valve assembly operations but that is a subject for another day and another blog entry.

The assembled valves we saw in the last blog entry when received back at the parent factory are given a final visual inspection and then each inserted in an open ended  glass envelope.  Here in the photo above, we see Candace Humpleberry casting a critical eye over a tray of assembled cages.

Now we come to the bit where the valve base and the electrode cage are married together.  It was vitally important that the cage and base were in perfect alignment otherwise the assembly would not fit centrally within the glass envelope and hence a perfect seal betwen base and envelope would be difficult if not impossible to achieve. Correct alignment was ensured at Mullard by making three key welded connections whilst the base and cage were held in a precision jig as shown in the picture below: -  As you can see, these jigs were beautiful precision pieces wrought by...

As well as the production testing we discussed in a recent blog entry, Mullard employed Quality Control (QC) testing where a sample of ten valves were taken at regular intervals  and subjected to a range of tests.  These tests differed from the production tests which were go/no-go type in that the QC tests were quantitative and the results were recorded using a series of Shewart Charts to individually log test characteristics both within a single batch and also inter batch. The Shewart Chart is a time related plot which allowed trends in measurement to be monitored.  The chart would have...