Here is an electronic engineers perspective on Cryo'ing Tubes.
Effect on Vacuum Tubes?Two different crystal structures that occur in steel which have absolutely no measurable effect on tone.
So cryogenic treatment works to improve the hardness of ferrous metals such as steel, but what about a vacuum tube – a tube is not a lump of steel – it’s a delicate and complex component made up of many different materials. The metal electrodes are mainly nickel for the plates and heater cover, titanium for the heater wire, molybdenum for the grid wire and copper support posts. The heater is coated with strontium/barium oxides. The electrodes are supported by mica washers within a glass envelope.
One can only guess as to what effect cooling a tube down to so such low temperatures will do to it as there’s been no serious scientific research investigation into this. Additionally, tube vendors have done little in the way of publishing noise measurement figures and life tests comparing treated and untreated tubes.
Typically all you’ll find are references to surface hardening, maybe nice magnified images of the surface of cryogenically treated steel and even rhetoric about NASA and Einstein on vendor websites. All this is about as relevant to your guitar tone as the colour of your guitar cable or your underwear. Could it be that cryo-treatment is pants?
I did find several scientific papers indicating that cryogenic treatment hardens aluminium. Perhaps it hardens copper, nickel and the other metals used in the construction of tubes too. Although there are no moving parts in a tube and no mechanical wear, hardening the electrodes would theoretically make them stiffer. Stiff electrode structure is good thing in a tube as it should reduce microphnony, which is caused by the electrodes moving relative to one another.
However let’s keep this in context. Cryogenic treatment is just a finishing process used to complete the conversion of austenite to martensite in steel as described earlier. The metal components inside a tube aren’t quenched to make them super hard in the first place so there is no conversion to complete. At this level cryogenic treatment achieves nothing and I’m inclined to think that it could potentially damage the tube.
Cooling a tube to cryogenic temperatures would put undue thermal stress on the glass envelope and delicate internal parts. The manufacturers never designed or specified tubes to be stored at such low temperatures. The act of putting one of these delicate devices through cryogenic treatment will cause contraction and expansion of the different materials and increase the chance of loosening some of the internal parts. The mica may no longer stay in secure contact with the glass envelope causing the tube to become more microphonic.
Cheers George
