Tell your dad that you want a Marshall stack, take him to the music store, and then start playing the sickest Nu-Metal you can think of throughout the store. Then tell him you put a down payment on the stack. Your Dad will surely be happy to compromise and agree to the purchase of the 30 watt Marshall instead. Or worse, tell him that you're thinking of switching to the drums !!! Seriously though, why do you need your dad to buy you a new amp? Get a part time job, save up your money, and buy it yourself. I believe fourteen is old enough to get working papers.