You need to have the unspent mana before the ability resolves. The ability doesn't allow you to activate mana abilities while it's resolving.
01-12-2004
wotc
The artifact's mana value must be exactly equal to the amount of unspent mana you have when the ability resolves. If there's less mana or more mana, the artifact won't be destroyed.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.