
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1897-1898
1903
1907
1904
1901
1910
1900
1903
1915
1900
circa 1900
1912
1906
1902
1910
1910
1914
1895
1896
after 1903
1910
1904
1908
1909
circa 1905
1912
1918
1915
1899
1905
1896
1904-1914
1901
1898
1917
1901
1902
1896
1906
1907-1917
1907-1917
1907-1917
1897
1907
1913
1898-1908
1901-1913
1914-1918