The UX-201 Triode

UX-201/301/401. The UX201 is one of the very first tubes ever marketed by RCA, coming online in 1925 and having the new UX four pin base. This is an incredible tube that has a detailed and warm sound boosted by the thorium tungsten filament. These were made in great number in only a few years and appeared in early radios. They’ve found new use in hifi preamplifiers and in such role they are very special. These tubes do tend to be microphonic and care must be taken to physically isolate them. They are worth the trouble though, and are one of the finest sounding tubes ever made. Tube data for the UX201 can be found here.