THE GREAT MULLARD MAGIC BLOG — mullard

The DM70 was quite a departure from previous tuning indicator/magic eye/ tune-on designs and was designed specifically with the portable dry battery receiver in mind but additionally was specified as an inexpensive device for the mains receiver too, not to mention as the reading indicator for a range of Negretti & Zambra high precision aneroid barometers made for the Royal Navy and Royal Air Force - in fact if you take a look at our product listings, you'll see a range of these barometers for sale!!!. The DM70 has a subminiture envelope and is constructed as a wire ended triode...

I was struck by the contrast between recent snowy weather conditions and this heartwarming nostalgic picture from the Mullard booklet of 1930, "How To Get Better Radio."   Whatever you are up to this evening I do hope you are not sheltering in the lee of a wall whilst listening to the light programme via your SG Brown headphones.....brrrrrr.

Today, we are going to talk about photocells  and in particular 'gas amplification,' an interesting phenomenon shown by gas filled photocells and  I was reminded of a hilarious occurrence when a vintage radio 'expert/forum gobs__t' proudly visited proclaiming that he had just 'stolen' a Baird Televisor lamp and on proudly producing it with a smug flourish, I was able to deflate his arch sense of triumph by regrettably informing him that in actuality he had 'stolen' a Mullard 56CG photocell. With photocells, although the manufacturing methodology is the same as for a standard thermionic valve,  a precise aliquot of a noble (inert) gas...

Mullard used a few dodges to ensure that blemished face plates were not used in tube manufacture such as when fitting the EHT connection in the cone of the 12 inch tube, this would always be located immediately above the gather or shear marks so that when the tube was fitted in the set, the tube mask would hide these marks - pretty clever. Otherwise, it was a matter of 100% inspection and selection and this is how it was done.   Firstly, only blemishes which could be seen from a distance of  3 feet 6 inches distance either under...

Today, let's look at the process for tube screen (or faceplate) manufacture that was employed by Mullard in the early 1950s.   If we had visited Mullard's tube manufacturing area we would have seen a tank holding 250 tons of molten glass and nearby, a work bench holding moulds which were contoured to match the required screen shape.   Glass blowers working in this area armed with iron rods, topped with a ball of fire clay would dip their implement into the molten glass tank and withdraw a bolus of molten glass known as a 'gather'.    The 'gather' would be held...