
De Forest audion 1906-1915
1906-1915
1906-1915
1839 (original); circa 1988 (replica)
1923
1903
1907
1904
1920
1910-1920
circa 1910
1914-1920
1914-1918
1910
1922
1955; 1830
1915-1917
1903
1914
1907-1920
1914-1918
1918
1915-1918
1913-1923
1916-1917
1926
1914
1914-1918
1912-1922
1915-1925
1904-1914
1920-1925
1906
1917
1906
1915
1910
1920-1925
1917
1910
1918
1907-1917
1907-1917
1925
1907-1917
1924
1903
1915
1926
1922-1923
1922-1923
1921