How would I replace values over a specified threshold with a specific value in a list?

I'm just kindof picking up grasshopper for my Masters of Architecture thesis and I'm having a problem figuring out the replace operator.

I have a set of lists in which I wish to replace all the numbers greater than 150 with 0. In my mind I need to find all the positions in the list that have values over 150, and then modify the original list to replace the numbers at those positions with 0. I can use the greaterthan command to create a list of true/false for each index position as to wether the value there is greater than 150, but I can't get this list to work with replace operator, which is what I think I need to do?

So essentially I've tried to use the greater than operator to create an index which I plug into the list's replace operator but it doesn't seem to work right. I don't think I really understand how the replace operator works. In some organizations I get it to replace the first two (index 0 and 1) with 0, but I can't seem to get it to replace all the "true" from the greater than index with 0.

I'm posting this on a computer without rhino/grasshopper because my laptop battery died and I don't have my power cord, so I can't post a screen capture of what I've tried. It seems like it should be a fairly basic problem though.

thanks for any help you can offer.