Arcturus is the name most closely associated with blue glass valves. This exhibit is a tetrode and dates from 1929 when Arcturus re-designated its type 122 as the 124 to match RCA with the UY224.
The UY-224 was the first USA AC (indirect) heater screen-grid or tetrode
The mesh screening cylinder and top disc. In the centre can be seen the control grid, cathode tube and insulated heater.
On the left can be seen the two heater wires enter the white insulation and on the right the glass rod that holds the support struts is seen behind the central electrodes. The pig-tail grid connection to the top cap is also easy to see.
The balloon envelope is 44 mm in diameter, and excluding the UX5 base pins is 107 mm tall.
References: 3002 & 1047. Type 124 was first introduced in 1927.