Hi Sephalix,
Thank you a lot for your input. greatly appreciated!
I keep some hope for the silverish tube...
wait and see.
I am right know checking carefully this tube. when looking through it in ambient light, i can say also that the silverish photocathode has also a very light brownish nuance and is translucid (i can see the internal (i guess) focusing electrode).
The silverish tube has also an internal serial number carved on the body of an electrode (the focusing one, big chance): 042229
The blueish tube has also an internal serial number carved on the body of the electrode (the focusing one, big chance): 5080960
I may suppose from that the silverish tube is older than the blueish one.
Wait and see.
Regards.
Lambda