The De Forest DL series first appeared in 1926. The L references the change to the UX4 base.
The DL-5 was designed as an AF amplifier.
The transit can for the DL-5. It can be seen that an earlier container has been used with a paper label covering the original details.
Thanks to Joe Gruber for sending the images.
The envelope is 32 mm in diameter and, excluding the UX4 base pins, is mm tall.
Reference: Bill Condon & Joe Gruber.
Absolute Maximum Operating Conditions¶
Updated September 22, 2020. shape:wide.glass.tube construction:pinch type:triode age:1920.1930 base:ux4 heater:5.0v pins:4 pin: