04-09-2017, 06:14 PM
Don't condemn that rattling 42 tube quite yet. Check if you can see what is rattling and if it is visible inside the glass envelope.
If you don't actually see a piece of metal or glass inside, its probably a loose piece of cement inside the bakelite base. Sometimes a lump of the cement that fastens the base to the glass envelope breaks loose and rattles around when you shake the tube, in which case it is harmless and nothing to worry about.
As Simplex mentioned, a dark spot inside the glass just above the base is normal on later production replacement tubes. The original tubes had the silvery mirror getter flash, while later tubes have the dark deposit. If the dark spot turns milky white, then you have something to worry about, as air has entered the tube and there is no more vacuum.
If you don't actually see a piece of metal or glass inside, its probably a loose piece of cement inside the bakelite base. Sometimes a lump of the cement that fastens the base to the glass envelope breaks loose and rattles around when you shake the tube, in which case it is harmless and nothing to worry about.
As Simplex mentioned, a dark spot inside the glass just above the base is normal on later production replacement tubes. The original tubes had the silvery mirror getter flash, while later tubes have the dark deposit. If the dark spot turns milky white, then you have something to worry about, as air has entered the tube and there is no more vacuum.
