TESLA ECF82 "NOS" 9 pin, 6.3V. Made in Czech Republic. Equivalent to the 6U8.
ECF82 TESLA TRIODE-PENTODE FREQUENCY CONVERTER VACUUM TUBE = 6U8. It was also found to be effective as an audio phase splitter. The anode opposite the grid support rods is open allowing a limited view inside. The bright structure is the beam forming plate. The ECF82 is a beam tetrode.