The site employed almost 7000 people amongst which were all kinds of specialists including physicists, chemists and metallurgists, resources far beyond the small handful of eastern tube factories that serve the guitar industry today. If there had been anything in cryo-treatment then surely Mullard must have known about it. Perhaps they did; perhaps somewhere, buried in some university basement, library or an old radio ham’s attic, is a technical paper written by a Mullard engineer in the early 1960s titled ‘An Investigation into the Effect of Cryogenic Temperatures on Thermionic Emission’. I’ll leave it to the reader to decide how long the odds are of that paper ever seeing the light of day and if it would put the big freeze on the cryo-treatment industry for vacuum tubes.
The vacuum tube industry today certainly does seem to suffer from more than its fair share of marketing hype. Like the washing-up powder market, the tube market is awash (sorry!) with all sorts of flimflam, not just cryo-treatment, but tube dampers, tube coolers and even rebranding modern manufacture tubesunder the names of once great manufacturers—cheap (sometimes not so cheap) gimmicks that are no substitute for real engineering. All this marketeering noise and nonsense achieves is to make the task of purchasing a good quality tube more challenging than it really should be. So, my advice when buying tubes would simply be this: invest in tubes from a reputable vendor that checks and matches them on a tube tester and guarantees them or, better still, seek out vintage N.O.S. vacuum tubes made by the likes of Mullard, Sylvania or the other giants from the golden age of tube manufacturing—we’re fortunate that they are still supplies of N.O.S. tubes available and there are deals to be had.
On a final note, the best means of avoiding being duped by marketing hype is to educate yourself. I can highly recommend taking a look at Materials and Techniques for Electron Tubes (1960) by Walter H. Kohl the Senior Engineering Specialist of Special Tube Operations at Sylvania and Electron Tube Design by RCA (1962). You’ll find nothing about cryo-treatment in these texts only information relating to the construction methods and quality of materials, that is, the stuff that’s genuinely relevant in the design of a good quality tube, and, these texts also provide a fascinating, nostalgic glimpse into the world of the 1960s, a time when manufacturers went to unprecedented lengths to design and construct tubes that were as near perfect as possible. After an hour or so’s reading from either book you’ll be in the know, a bona fide tube guru knowing what’s important in tube design and, what’s not so important.
There is variation in the noise and microphony of vacuum tubes because of engineering limitations or to put it another way, tube manufacturers’ ability to accurately and consistently fabricate these complex devices. Mullard (or perhaps it was Sylvania) in their heyday, with vast resources and a wealth of expertise at their disposal got as close as anyone to manufacturing the perfect vacuum tube, however even their tubes were subject to variance in component tolerances which allow electrode movement and sensitivity to microphonic pickup; DC leakage paths in the mica insulation spacers that allow small currents to flow where they shouldn’t and fluctuations in thermionic emission from the cathode oxide coatings, both of which result in self-noise. It would be magical if cryogenic treatment were some kind of ‘silver bullet’ that improves the insulation properties of mica spacers, reduces inter-electrode movement and improves the emission of the cathode coatings to reduce noise and microphony. But I cannot begin to imagine how this works—’magical’ really is the right word to use here because cryogenic treatment of tubes certainly isn’t science—there are no well-considered explanations describing how the cryogenic process works to improve the electrical characteristics of a tube or even the most sparse comparative test results to validate claims for improved performance. The bottom line is that cryogenic treatment is no remedy for inferior materials or defects in tube construction and it won’t transform a rebranded modern manufacture tube into a genuine N.O.S. Mullard a or Sylvania tube—it just doesn’t work that way.
If you’re interested in what the Mullard Blackburn factory was like in its glory days then do take a look at the following article ‘Speed, Efficiency & Perfection – Aims That Have Built a Mammoth Factory in 16 Years’ originally published in 1954 in the ‘Blackburn Times’ not long after the factory opened.
