Artifact Details


3N21 Germanium tetrode

Catalog Number



Physical Object



Identifying Numbers

Model number 3N21


overall: 2 in x 3/8 in x 1/8 in


The object has four leads.

Per Jack Ward, Transistor Museum
"Sylvania 3N21 (1 piece), germanium tetrode transistor. Mid-1950s. The earliest junction transistors performed better than the original point contact transistors in all respects except one – frequency response. Whether grown junction or alloy, the first junction transistors were very limited in terms in effective operating frequency. This limitation was overcome in a number of ways, including the use of a fourth electrode attached to the base of the transistor. By proper use of bias voltages on this additional base lead, the transistor could be made to effectively operate up to 15MHZ, which was fairly impressive for this timeframe. Several companies offered these four lead (tetrode) transistors, including Western Electric (3N22), Texas Instruments (3N34/35) and GE (3N36/37), and the Sylvania 3N21 included in this collection. The “3N” designation for the tetrode transistors represents the general approach of: “N” number + 1 = the actual number of leads, so 3N + 1 = 4; four leads on a tetrode. Rare – these four lead (tetrode) transistors were in production for only a few years, with low volume production. This device represents a unique and short-lived transistor technology from the mid-1950s."



Collection Title

The Paul Sullivan Collection of Early Semiconductors


Gift of Pat Sullivan Belotti

Lot Number