|
The black blotches are called getters and are normal in tubes of any age...During manufacture they use high power to vaporize magnesium or similar reactive metals so they form a coating on the glass. That coating sucks up any remaining/newly freed gas molecules that otherwise would contaminate the vacuum.
BTW a good way to tell if a tube no longer is under vacuum is if the getter turns white.
Typically a 4 wire tubular cardboard lytic has 3 caps with a shared negative, but there are exceptions....The values and wire color code should be on the cap's label...Read it.
|