THE GREAT MULLARD MAGIC BLOG — mullard

With the electrode cage sorted, the next stage was to prepare the valve base.  In the valve build described - the DF91 - this has a B7G glass base, the manufacture of which was the subject of an earlier blog entry where we left the valve base as a glass button having seven composite wires, each comprising of a valve pin, a seal and an electrode support wire, all very nice, but an electrode cage cannot be mounted on the valve base as it stands. The valve base prep team had to first prepare the base using a special machine...

We last left valve assembly where we had formed the electrode cage, today, we will describe what happened next in the valve assembly process.  Before the electrode cage could be mounted on the valve base, four additional components needed to be added and welded into position.  The first two components were the top and bottom screen plates and projecting tags which are welded through onto tags on the outer screen as per the photo below: -  The third extra component is an L shaped piece of metal which is first welded to the bottom screen plate and then bent over...

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...

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...

Well, we're going to talk about the ECC81 twin triode today, originally designed for TV applications, yes, that's right - TV!!!!     All the other valves we have discussed in this World Series of blog entries had been designed for use at the then used British TV frequency bands of 45 - 70 MHz.  However, other countries used carrier frequencies at a much higher range within the 100 - 300MHz region at which a low noise level high grade triode would be needed so enter stage left.... the ECC81.  The ECC81 was great because it was inherently a 'low...