Z5600M stamped "ungültig"

[kay486]

Hello there, i just bought four Z5600M tubes in original boxes, never used (i was even the first one to open them). They all work just fine, except for one wich has some blue parasitic glow on few of the wires. The thing is, there is "ungültig" stamp on all of the boxes. Im not really sure what it means, google translate isnt too specific. But im guessing it means that they are expired maybe? If so, whats the reason to stamp something like that on tubes, i mean, wouldnt all of the tubes be expired by now?
Im just interested in the story behind this, how things were done in the past days :)

[Dekatron42]

It means "invalid" - I have a few of those too and also a few which says "unverkäuflig" which means unsaleable - not for sale. All of mine were bought as "laboratory samples" so I guess that yours are too or that they are factory rejects.

 

/Martin