Weights on a preamp

In some cases it can work depending on the gear involved, the type of stand used, or other factors. I used to place a VPI brick on top of my Spendor 1/2e speakers and they helped stabilize the speaker/stand interface. However, I find that I don't need to use any weight on my Audio Kinesis Stormbringer speakers.

I also used the bricks on my amp to some good effect, but it was a marginal difference compared with the speakers. Only way to know for sure is to try it out. Of course your selection of weight materials will also have an effect. Lead sacks seem to work well. Fine sand placed in plastic zip lock backs also are a good starting point and cheap to use for a test. Good luck and let us know what you find out.

I have dampeners on all cases. Some are heavy, some just size 10 rubber bottle stoppers.
It is 'nearly free, and I like it. I make no claim that it makes any difference... Though I do prefer the sound with them on...

More than almost any other kind of electronic component, because they contain small signal tubes that are often microphonic, a tube linestage is prone to problems with vibration. It certainly does not hurt to try different forms of dampening. I personally like coupling the component to a good vibration dampening shelf, but, it makes sense to experiment with any and all of these choices.