
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1923
1903
1907
1904
1901
1910
1922
1900
1903
1913-1923
1915
1900
1914-1920
circa 1900
1920-1929
1912
1931
1906
1902
1930
circa 1930
1910
1910
1901-1930
1925
1928
1914
after 1903
1910
1927
1924
1904
1908
circa 1930
1909
circa 1905
1912
1918
1915
1905
1904-1914
1901
1931
1917
1901
1902
1927
1906