
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1903
1907
1904
1901
1910
1900
1903
1915
1900
1914-1920
circa 1900
1912
1906
1902
1910
1910
1914
after 1903
1910
1904
1908
1909
circa 1905
1912
1918
1915
1905
1904-1914
1901
1917
1901
1902
1906
1907-1917
1907-1917
1907-1917
1920
1907
1913
1901-1913
1914-1918
1914-1918
1872 (original); 1909 (model)
1919
1915
1915
1901
1911