
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1903
1907
1904
1901
circa 1910
circa 1900
1910
1900
1955; 1830
1915-1917
1903
1914
1901
1916-1917
1900-1910
1900
1914
1904-1914
1901
1906
1917
1901
1902
1902
1906
1915
1910
1917
1910
1907-1917
1907-1917
1907-1917
1903
1915
1900-1909
1901-1910
1906-1916
1903
1906
1904
1900-1910
1901
1900-1910
1915
1900-1910
1900
1900-1910
1934