GNM-69 was a homemade (but FCC type-accepted) power amplifier for WUVT-FM acquired from Georgia Tech, which increased the FM's power to 735 Watts.

From John Lyles:

The GNM-69 Xmitter was 430 watts into a 4CX300A tetrode. I lived with the GNM-69 for a few frightening years, as it would shoot fire out of the front plate current meter, whenever the tube socket would arcdown. We were insane, working nights alone, on top of Lee Hall with a 2x4 smashing snow off the antenna so that the screen power supply fuse wouldn't blow.

The GNM stood for Geoffrey N. Mendenhall, its builder at Georgia Tech. In the April 28, 1999 edition of Radio World is an article that he was receiving the 1999 NAB Radio Engineering Achievement Award. He is a vice president at Harris Broadcast Systems in Quincy, IL.

From the Radio World article:

Mendenhall, 52, began his broadcast career in 1963 while still in high school as a part-time broadcast technician. He helped pay his way through college by working for several Atlanta broadcasters before graduating from the Georgia Institute of Technology in 1970.

Click here for more on the GNM-69.