Haven't read the whole thread but a transponder should be always ON.
If it is Mode C it should always be in ALT mode, unless otherwise requested by ATC.
To do otherwise is just nuts, because it makes a Traffic Service practically worthless so all you are doing is screwing others, and preventing TCAS systems seeing you, so you are not doing yourself any favours.
Yet loads of pilots continue to do it.
BTW transponders used a travelling wave tube, not a magnetron which is used for shorter wavelengths (radar). All modern transponders are solid state.