HP and logimetrics units do this. Only the HP one that works at a higher potential does this (the C band unit) the logimetrics is unknown, solid state, and S band.
i noticed the HP units < C band run at ~1kV, while the C band unit runs at ~2kV.
If I figure out the potentials of the logimetics units, which runs at 2-4GHz (s band), maybe we can say this phenomena only happens at potentials <<1kV. , but right now it seems common to a logimetrics unit, which runs 2-4ghz, and a HP tube unit, that runs 4-8ghz.
they both have line power and rf power switches. the HP one is well documented 49X series, made in the 60's or something, and the logimetirics I have NO idea. Can't find shit about it. Not sure if i want to take it apart.
I also have some hughes units that I need to take a look at.
I did not see a spark gap in the HP unit that I took apart... only some vacuum tubes, vacuum tube relays and vacuum tube voltage reference, plus a few transistors.
Ima look at the schematics (one of my HP S band amplifiers burned up recently.. unsure of where the smoke came from), so I will look for damage and try to see if I find evidence of a spark gap. I think pot for helix current was bad and I was running it in over drive for a while, then I put in the wrong sized fuse
very much hope that the TWT is ok in that poor guy
, hopefully the testequipment reaper does not show up.