The Tekade VT126 is an early double triode. The filaments are oxide coated and the valve fits into a special six pin base. The above adverts claims loud speaker strength output using just one VT126.
The circuit configuration would most probably be a two stage transformer coupled design.
The trade name Pentatron appears on one of the bright anodes.
The other anode is stamped VT126 and has the KTD logo.
The anodes are mounted side by side and are formed as open U shaped channels. The filament tensioning springs can be seen above the anodes and connect to a single central support.
Here the single inverted V filaments can be seen within the ladder grids.
The base is a special design with five pins arranged at the points of a pentagon and the sixth placed in the centre. The base is stamped with the KTD logo.
Enhancing this image revealed the ingrained dirt on the glass as well as the structure of the grids. Each grid has been stamped from a single thin sheet and then folded over with a support at the fold.
In this monochrome image the one and a half turn spring in the filament support can be seen together with more detail of the grid construction.
The filament wires are mounted to the supports with a small piece of tape that looks to be spot welded to the support. It is not clear if the wires are welded or just held mechanically by the tape to strut weld. If the filament core is tungsten wire then the latter is the most probable.
The VT126 cam complete with what looked to be a valve holder, however, closer inspection shows it to be a base adaptor. The VT126 pins are special not a common base type. The red rings denote the anode connections with the electrode identification stamped into the Bakelite moulding.
From the side the form of the adaptor can be seen. The brass pins looked to have been turned from tube to form the slight outward curve needed to grip the socket. Side slots have been machined to give the tube slight compressibility.
The underside with the hexagonal arrangement of the pins.
The balloon envelope is 40 mm in diameter and, excluding the base pins, is 101 mm tall.
Reference: 3002. Type VT126_TKD was first introduced in 1926. See also1926 adverts.