The ECC83A is a modern copy of the classic audio double triode. It is designed for high gain and low current and is typically found at the front of an audio amplifier as voltage amplifier and/or phase splitter.
Bugera is an amplifier manufacturer. Their web site states that they buy in valves and state that they reject 90% on test.
The construction is as two separate triode sections but additionally there is a screen plate passing between the sections. This sheet connects to the getter holder but not to any electrode or external pin. The heater centre tap connected to pin 9 connects to a shield under the lower mica.
One of the triode sections.
The triode sections close-up. A square plate connected to the cathode sits on top of the lower mica and an identical plate is fixed to the underside of the first top mica. The 'A' variant seems to be the enhanced shielding.
The thin glass tube envelope is 22 mm in diameter, and excluding the B9A base pins is 50 mm tall.
Reference: Datasheet. Type ECC83A was first introduced in 2000.