This part is a kind of semiconductor called EL34.

Function of this product has High Performance Audio Power Pentode.

Manufacturers : Svetlana

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Some of the text within the PDF file :

SVETLANA TECHNICAL DATA EL34/6CA7 High Performance Audio Power Characteristics T Pentode he Svetlana™ EL34 is a glass envelope power pentode having a plate dissipation rating of 25 Watts with convection cooling. It is intended for audio frequency power amplification service in either pentode, ultralinear or triode connection and single or push-pull/parallel applications. The Svetlana EL34 has an indirectly-heated oxide cathode, which may be DC operated for the absolute best hum/noise performance. The Svetlana EL34 plate is made from a laminated material that improves heat transfer and has superior performance under overload conditions which are often seen with guitar amplifi- ers. Close manufacturing specification tolerances and improved processing provide enhanced reliabilit [ ... ]

EL34 PDF Datasheet Download