Viacom’s largest holder raised its stake to 19.5%.

National Amusements Inc., which has indicated its unhappiness with the price offered shareholders in the pending buyout of Viacom International, said it had raised its stake in the entertainment and communications concern from 18.3%. The Dedham, Mass.-based theater chain said it has sought Federal Trade Commission clearance to raise the stake up to 49.9% from the current level. National Amusements said it will continue to study alternatives to the $2.9-billion buyout proposal, including a possible offer by the company or an investor group led by it.