The CV553 (commercially the 25L6GT) is designed for use in single ended audio stages in apparatus using a 300 mA series heater chain. As a single ended audio amplifier it can produce 4.3 Watts.
The Brimar logo on the base cap.
Looking at the top mica components. There are many heater strands in the cathode as one would expect from 25 Volts. The copper control grid supports have a large U shaped heat sink on top.
The wide glass envelope is 29 mm in diameter and, excluding the IO base pins, is 71 mm tall.
