The Audion: Grid Control and the Circuit

Start with the device drawing

In De Forest’s patent, look for the heated element, the electrode that collects current and the additional electrode between them. The third electrode can affect the current without itself being the output. An original tube record gives a second way to identify the device, though a museum object does not report its behaviour at every operating point.

The distinction between control and output is a useful first step. Label a small input that changes a condition in the tube. Then label the current whose change might be used elsewhere in a circuit. The explanation becomes more precise when it specifies which quantity the engineer is observing.

Sources for this section: [1] · [2]

Put the wiring on a different page

Armstrong’s experimental detector places an Audion in a circuit with a route back toward the input. That arrangement can reinforce a received signal. The tube contributes a controllable electrical response; the wiring establishes the route through which part of the response returns. Changing the external wiring can change what the system does while leaving the internal tube intact.

Read the patent for the device and the other object record for the assembly. A description of the assembly cannot be derived from a photograph of an unconnected tube.

Sources for this section: [2] · [3]

Practice assigning a claim

Imagine that a collection contains a loose tube, a wiring diagram and a dated observation of a station received more clearly. Assign each record a job. The tube can help identify components. The diagram can show the intended circuit relation. The dated observation can support the result, provided it identifies the setup that was tested. This exercise prevents the effect of the system from being credited automatically to a single component.