See manual here:

https://www.radioelec.com/images/Image/ERSATZ%20TRIODE_english.pdf

Characteristics :

- Old triode ersatz module
- Small dimensions allow it to be easily inserted into the circuit or into the tube base.

- The connections are simple:

1 wire to connect to the grid pin

1 wire to connect to the pin Plate

1 wire to be connected to ground or to a filament terminal

- A small potentiometer allows to adjust the gain

- Module dimensions: Diameter 20 mm, max thickness 10 mm

- Compatibility:

Plate voltage 30 to 150 V
Amplification: 1 to 20 (adjustable)
"Plate" current: 1 to 6.5 mA

Composition:
- Comes with instructions and connection details

Use :
- Circuit for electrically replacing triodes type A405 - A409 - A410 - B410, probably also triodes TM, ...