The Telefunken AD1 from 1935 is a directly heated audio output triode. In a single ended configuration the output is 4.2 Watts. A pair in push-pull can output 9.5 Watts.
The shape of the anode is similar to the original design of the PX4 triode and the performance is approximately the same.
The Telefunken logo and Type designation AD1. There are six filament loops passing through the grid. The PX4 has four.
This side of the anode has the glass electrode support rod and a small pair of flanges for extra heat dissipation.
The glass rod with supports for the tension springs.
Above the pinch and hard to see is the start of the grid winding.
The classic envelope is 58 mm in diameter, and excluding the Ct8 base pins is 124 mm tall.
Reference: Data-sheet. Type AD1 was first introduced in 1935. See also1935 adverts.
