Edison Swan thermionic triode valve
1932
1932
1918
1925
1928
1935
circa 1920
1927
1925
1927
1930
circa 1920s-1930s
1928
1923
1923
1923
1935
circa 1930
1923
1925
1922
1927
1924
1930
1925
1923
1923
1923
1930
1928
1928/9
1925
1923/4
1930
1927
1927
1923
1925
1923/4
1931