CREATE TABLE table_51809 ("Name" TEXT, "Built" TEXT, "Wheels" TEXT, "Fuel/ Trans" TEXT, "Status" TEXT, "Colour" TEXT)

What is the manufacturer, found under the Built column, that made locomotives with a Fuel/Trans of diesel-electric?
SELECT "Built" FROM table_51809 WHERE "Fuel/ Trans" = 'diesel-electric'
SELECT "Built" FROM "table_51809" WHERE "Fuel/ Trans" = 'diesel-electric'