El84 / 6bq5

The EL84 (European designation - known as the 6BQ5 in North America) is a vacuum tube (a.k.a. valve) of the power pentode type. It has a 9 pin miniature base and is found mainly in the final output stages of amplification circuits, most commonly now in guitar amplifiers, but originally in radios and many other devices of the pre-transistor era.

Equivalents or near equivalent:
6P14P (Cyrillic: 614) made in the USSR.