RCA units..
These were made by a company called T-K., short for Terro and Kift, referred to as "Monotubes", Frigidaire either bought there units from them or liscense built them, Admiral,Some Kelvinators as wll as Universal all used them...Oh yeah, Philco did also, To my mind ,very good units, a tad slower than Calrods, but longer lasting and more even..IMHO!