An oil-filled 5kW mod trans from Electro Engineering. When I got it the insulators were broken, so I opened it up. Some mineral oil, and a LOT of sand. Makes sense, as they were in Cali...maybe in the beach? Turns out they did it to cut back on the "talking" mod trans sometimes do. Didn't work, as this was a really noisy TX when I babysat it back in the early 80's 73DG ps...It drove a single 5CX5000 via two 4-1000's.