Well, for sure, if it's in a combo-amp that rattles with speaker movement, that can't be good...but neither is your/our obsesssion with thing, checking it out, pulling it out of the socket over and over. I've had tubes that were like that their entire lives, at least, during the time I've owned them. I try to stick them in a piece of test gear, if possible.
You will note at some point there are two basic methods of building octal tubes: One (older) crimps ALL the incoming wires together in a glass wad underneath the plate structure. Like an incandescent light bulb. Those, while they are subject to loose-baseism, the bulb essentially hangs on a web of resilient copper wires and so there is a sort of shock absorber effect...for vibration, not for tugging the buld relative to the base. The newer style (which I and most people much prefer) is to have much thicker, ("pins" instead of "wires") individual glass-to-metal seals which you can see inside the tube. Far more rugged. But forget not that the old style worked for fifty years and gazillions of them work today.
Whatever you want to say about it, the failure of such a tube is 50 times more likely to occur via your/my hand tugging on the envelope rather than leaving it alone in its socket.
That said, if you have such silicone and can maybe heat it up a little if it's really thick (just leave the tube and the tube of silicone out in the sun, that's all, so it will flow & adhere a little better) I'd have no objection to running a thin bead around the base of a loose tube. Thin, small. Don't force it into anything, and it wouldn't hurt to wipe off the glass & base w/alcohol or solvent where they join to get finger-oil off. In other words, just stabilize, don't try to jam silicone into the empty space in the base. Not needed.
Topic: Loose tube base (Read 3935 times)