The Historical Study Collection of the Faculty of Electrical Engineering, Mathematics & Informatics (EWI) at the University of Twente [1] includes more than 1,100 devices from the history of the faculty's disciplines: electronic measuring instruments, computers, calculators, telecommunication equipment, etc. This equipment is managed by volunteers, mostly retired faculty members. This episode of Retronics is about valve testers of the AVO company, some of which are part of the Study Collection in question.