Yes, I know what they are. Reverse klystrons, repellers, what have you...

A friend found some and wants to know about their use, and maybe put them to use. What do I tell him?

The safest thing I can think of is a VFD.


(actual tube shown)

What a wicked looking torture implement! Actually they usually sell cheap as without the cavity, it is of no use, and probably would still be of no use with one. They are practically a display item, so owning one is enough!

Somewhere around here I have a subassembly that takes these. Without the fancy hardware that clamps them in position, you can't use them anyway. I remember unearthing some in the college EE junkbox, and the prof called them MacNally oscillators. I think I looked them up later and found NacNally had published the original paper on them, or else was mentioned in the appropriate Rad Lab book where they are described.

Sad when things get separated. 2nd time in the last couple of days, here. The other was a phasitron without its modulator coil.