At first glance, a problem is not obvious to me! (Other than the warped dial. But that's not really the air cap.) Give me a clue!
Not necessarily the cap itself, the unit as a whole and of what it contains.
Hmmm. It looks like a lot of "staining", perhaps because of mouse urine, but that is pretty typical!
The leftmost trimmer cap has most of the top plate missing....if this is it.
Well, I may be wrong, but page 16 of the 1937 Philco List Parts catalog on this site says the bulb bead should be white, indicating a 2.5 volt bulb, not a blue 6.8 volt bulb. The bulb voltage is taken right off the heater 2.5 ac line; I always thought it looked dimmer than it should be - and tried cleaning the socket to no avail.
Then your thread name is a bit misleading as the bulb is not a part of the cap. It jis mounted on the dial assembly which is then attached to it, but the cap ends where there is no longer stator, rotor, trimmer or the shaft.
There is then nothing really wrong with the cap.
The bulb...???
