Chinese Shuguang 6550B.
The beam power quadrupole 6550B has an anode limiting power of 35W (42W). In the audio amplifier, two tubes A1 and AB1 can be used for push-pull output and reach 100W power. The 6550B can also be used in an electronic voltage regulator circuit.

The 6550B is similar to the KT88 and can be used interchangeably.