The XH1.5 or XH1.5V miniature triode dates from 1935. The base is the Hivac small four pin, and the design use was for hearing aids but they were useful for miniature radios and radio controlled models.
Filament operation and anode supplies were both to be taken from dry calls.
Thanks to Martin G8BHC for donating this exhibit.
The anode side view.
Here the construction can be seen with the grid supports extending through both mica supports but the grid winding remaining mainly within the anode.
Here the filament can be seen as a single hairpin with the tension spring above the top mica.
The thin glass tube envelope is 15 mm in diameter and, excluding the base pins, is 59 mm tall.
Reference: 1020. Type XH1.5 was first introduced in 1935.