Monitor Products Company; Los Angeles: During WW2 Monitor Products made crystals for the military sector. Later they made at least a signal generator. In 2002 Monitor Products was bought out by MMD (mmdcomp.com). Monitor/Quartztek was founded in 1994 by Rodney M. Mills. HQ is in Rancho Santa Margarita, California, USA, MMD Monitor/Quartztek.

At least in 1946 Monitor Products made a signal generator for IF and RF, named Monitor Crystaliner. They made at least three models of the Crystaliner, the earliest with no power switch. At least some of them have a line cord resistor instead of a transformer. According to an ad in "Radio & Television Retailing", July 1946, the Crystaliner were sold by Metropolitan Electronic & Instrument Corp., 6 Murray Street, New York 7 - but probably also from other assorted vendors. This Crystaliner is a competition for the Bliley CCO-1A, another small multi-channel IF signal generator, which is also AC-DC.