PX4

The PX4 is another Marconi-Osram directly-heated power triode from the 1930s British tradition, rated for about 3.5W in single-ended operation. It shares the family resemblance of the PX25 but at lower power, with an intimate, detailed presentation that devotees consider superior to the 2A3 in triode purity. The 4V filament and UX4 base distinguish it from American types, and its low plate resistance (~1040 ohms) provides good output transformer coupling. Genuine Osram and Mazda PX4s are exceedingly rare collector items, making this a tube for the dedicated connoisseur.