Each sunday Willem van Twillert plays in the services in the Johanneskerk in Amersfoort.
In the church is a small Van Vulpen-positif of 5 ranks.

Specification:

Manuaal	C - f'''
Holpijp	8'
Prestant	4'
Fluit	4'
Octaaf	2
Mixtuur	II B/D

Pedaal: aangehangen (C - d1)