Re: Cold and valves
Pinch seal and wire ended valves are much less prone to going to air in low temperatures. The mechanism of the phenomenon with glass miniature types being particularly, but not exclusively prone, is due to the connection pin reducing in size as it enters the glass seal. In some types the the sealing interface is stressed by the shoulder to the point that it eases the wire and breaks the vacuum.
A known problem in early avionics using valves in such style as the EF50. Early equipment would be switched on and warmed up before take off to stop failures at altitude.
Commodity valves as used in TV and radio, normally don't often suffer in normal conditions, but the garden shed as Paul has pointed out may over time experience perhaps 50°C gradient. Eventually the valve will go to air with no immediately visible damage.
Greg.
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