The valve with the white top is faulty.
There is an air leak.
From the web......
White getter on a bad tube VS a healthy tube getter
The second thing to look for is the condition of the getter. This is the greyish coating usually found at the top of a tube, but can be on the sides, or both top and sides, depending upon the tube type. Any color from grey/silver, to black is healthy. When a vacuum tube develops an air leak (a small crack or bad seal by a pin for example) this getter color will change to pure white.
Hope this helps.