do vacuum tube devices (microwave) act as parasitic frequency mixers?

[CopperCone]

Do microwave buffer amplifiers (Traveling wave tubes) act as mixers? (i.e. unwanted signal going into them and being mixed into some other frequency).

Do they act like mixers that make more 3rd harmonic then 2nd harmonic (since they have corrosive metal (do they?) in them) but no PN junctions?

Or does some other effect take place?

[CopperCone]

well, as far as power devices go they are the only approachable low budget solution for wide band power amplifiers (that tend to operate at 1 or 2 octaves)...

A solid state solution would run like, 20,000$... however with TWT you might only be buying a few minutes or hours of run time from them due to age.

[CopperCone]

btw, I am interested to know because I want to determine how much isolation (by isolators) is required to prevent harmonic generation for an experiment that I am conducting. I don't want 'crosstalk' between the amplifiers causing harmonic generation, as it is confusing the results of the non linear junction detector experiment.

If the device is known to be a horribly inefficient mixer, perhaps I can ease the isolation requirements (adding 80db of isolation at a high power level to a particular channel is rather pricey).