A commercial tube contained a cathode, two control grids (\(G_{1}\) and \(G_{2}\)) , and a collector electrode. The cathode was kept at a constant voltage (\(2.1V\)), and grid 1 and grid 2 were kept at constant voltages. (\(1.49V\) and \(13.998V\) respectively.) The anode current, (converted into \(V_{out}\)), oscillates as accelerating voltage \(U_{2}\) increases. The final Franck-Hertz curve for Argon shown in Figure 9 contained 5 dips of the anode current.