Vacuum tubes

The KT88 is a beam tetrode/kinkless tetrode (hence "KT") vacuum tube for audio amplification.

thumb|upright|A Mullard TDD4 valve. The gold spray coating served no purpose other than to hide the blackened interior, as Mullard valves were still manufactured using the azide process, long abandoned by other makers. upright|thumb|A Mullard EL34 power pentode thumb|An EL84 valve made in Russia in the 21st century

audio amplifier output stage coupling method

electrical and electronics plant in Saint Petersburg

French 1915 vacuum triode

The 12AU7 and its variants are miniature nine-pin (B9A base) medium-gain dual-triode vacuum tubes. It belongs to a large family of dual-triode vacuum tubes which share the same pinout (RETMA 9A). 12AU7 is also known in Europe under its Mullard–Philips tube designation ECC82. There are many equivalent tubes with different names, some identical, some designed for ruggedness, long life, or other characteristics; examples are the US military 5814A and the European special-quality ECC802 and E82CC.

real, perceived or claimed quality of sounds from vacuum tube amplifiers