Some years ago I purchased an old DeForest 504A radio tube from an elderly retired navy guy.

It;s quite rare I think and the one I have has never been used (the silvered interior is not present).

It's been packed in a box for a decade so I do hope it's still safe!

Interestingly these things were packed in a clever cuboid frame with springs emanating from the corners, this allowed them to be banged around while the delicate tube itself was suspended on these springs, very neat solution given the fragility of these things.

Here's a different tube but in the same kind of frame:

Seems the 504A was also "second sourced" by RCA as the 204A, here's that datasheet from 1927. The (EiMac 450TL) tube in the image above seems to have been around twenty years later - 1947.

 

Quite a find. Maybe one was used in Charles Lindbergh's communications in his flight to Paris in 1927, also same year that I was born. Could use a microwave transformer for your plate supply.

 

Is the silver coating white?

 

Is the silver coating white?

I don't think there's any sign of any kind of coating so I assumed it had never been used at all (I assumed further that its getter therefore was activated by first use - but this is guesswork).

 

I don't think there's any sign of any kind of coating so I assumed it had never been used at all (I assumed further that its getter therefore was activated by first use - but this is guesswork).

The getter gets activated when the tube is made to remove residual gas. If the inside glass surfaces are white (oxidized) instead of silver the tube is likely bad from air leakage.

I still have one or two systems that use tubes in shunt HV regulator supplies for ion electrodes.
https://forum.allaboutcircuits.com/threads/tube-creep.113198/post-880679