PX25

The PX25 is a British directly-heated power triode developed by Marconi-Osram (GEC/MOV) in the 1930s, delivering about 6-8W in single-ended Class A. It combines the tonal refinement of a 2A3 with greater power and a distinctly British midrange character that is lush without being syrupy. The tube's relatively low mu (~3.8) and low plate resistance make it very easy to drive but demanding of the output transformer. Original GEC PX25s are among the rarest and most expensive NOS audio tubes; current production from KR Audio and EML provide modern alternatives.