The Type 71a Triode

The Type 71a. This very early tube type dates to 1927 and makes 3/4 of one watt of power in a single ended circuit. Within its comfort zone, the 71a is absolutely one of the most musical sounding tubes ever made. The little brother of the 45, these were used in millions of radios from the 1920’s and were still in production until the early 1940s. The 71a has the ability to present a sense of space that is remarkable, and somehow different than its contemporaries. NOS examples of the globe and ST versions of this tube are still fairly plentiful, sometimes in their original cartons, and sound very good. Tube data for the 71a can be found here.

71a. Three globe shaped 71a tubes, by Sylvania, Cunningham and Arcturus. As is common in tubes of this era, each manufacturer has its own unique designation for the tube type, with Sylvania being an SX-171-A, Cunningham had the CX371-A and Arcturus was No.071A (RCA invented the tube and claimed UX-171a, with UX being the designator of the new four pin UX-4 tube socket). These are all 1920's tubes. Of the three I think the Arcturus is the better sounding (and looking) tube. The early Arcturus tubes always sound good to me; I think they must have been a high spec tube manufacturer to sell a blue glass tube in an era where the tube was hidden away in a cabinet and never even seen by the consumer.

71a. Quite a bit of difference in Sylvania's production. I'd guess the tube on the right is an earlier version and probably one of the earliest 71a made.

71a. Early Tung Sol engraved base. The test labels on some of the early tubes are a cool feature.