[Wendymott]

Sorry to "jump in" but no one has mentioned, most of these valves are possibly over 50 years old. Is there any information regarding the ability of glass and glass to metal to sustain its original quality over such a long time. I suspect valve manufacturers were only concerned with the "now" factor. Not expecting their products to be around 50 - 70 years in the future. Bit like the radio equipment used in WW2, not expected to survive more than a few weeks.