This exhibit is a CT-25+. The label shows a 5 and a + which makes the CT-25+ the only candidate. Also the CT-25+ is described as a low impedance output triode and the two sections in parallel is a way of reducing the impedance. CT-15 has a single small cylindrical electrode system and this looks like two such structures.
The detail picture shows the twin narrow bore anode assembly. Within each anode is a helical wire grid joined together by a round bar above the anode. The filament is a single strand passing vertically through the centre of each anode. Each support for the lower end of the filament is brought out to a base pin. The top connections are made to a supporting frame that at first sight passes through the pinch to a base pin. Close inspection reveals that the wire passing through the pinch is not connected. This puts both filament sections in series.
The wide glass tube envelope is 40 mm in diameter, and excluding the B4 base pins is 102 mm tall.
Reference: 1043. Type CT-25+ was first introduced in 1926.
Absolute Maximum Operating Conditions¶
Updated May 15, 2019. shape:wide.glass.tube construction:pinch type:triode age:1920.1930 base:b4 heater:5.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f