
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1923
1903
1907
1904
1910
1922
1903
1913-1923
1915
1914-1920
1920-1929
1912
1906
1910
1910
1925
1928
1914
after 1903
1910
1927
1924
1904
1908
1909
circa 1905
1912
1918
1915
1905
1904-1914
1917
1927
1906
1907-1917
1907-1917
1907-1917
1922-1923
1922-1923
1922-1923
1922-1923
1921-1926
1925
1920
1907
1913
1914-1918
1914-1918