OK, I stand corrected. I had heard of Maser but frankly did not understand it.
Just read a little about it and realized I was at a site once. I got the tour of the VLA site in Datil, NM when they had the first 3 dishes operational. They were using cryogenic receivers then. Then came along the GASFETs.
We visited the VLA in 2010 on our way back across the country.
Neat place!