The original Masco MA-25 was manufactured in 1947. The Masco that I own is a second generation MA-25P. The suffix is N indicating that it is a later model, probably mid 1950s. Masco stands for MArk Simpson COmpany. The company was in Long Island City, New York. The company later became Fanon/Masco.
The amplifier I have originally had a phonograph mounted atop but it was long gone when I got the amp. The output was rated at 25 watts. The output stage was cathode biased. The phase splitter was the anode follower type.
Here is the original schematic as best as I remember it.
Click on the image for a larger diagram suitable for printing.
The following is a photo of the identification plate on the back of my amplifier.