Thermionic valve in the context of Thermionic emission

In electronics, point-to-point construction is a non-automated technique for constructing circuits which was widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their introduction in the 1950s. Circuits using thermionic valves (vacuum tubes) were relatively large, relatively simple (the number of large, hot, expensive devices which needed replacing was minimised), and used large sockets, all of which made the PCB less obviously advantageous than with later complex semiconductor circuits. Point-to-point construction is still widespread in power electronics, where components are bulky and serviceability is a consideration, and to construct prototype equipment with few or heavy electronic components. A common practice, especially in older point-to-point construction, is to use the leads of components such as resistors and capacitors to bridge as much of the distance between connections as possible, reducing the need to add additional wire between the components.

Before point-to-point connection, electrical assemblies used screws or wire nuts to hold wires to an insulating wooden or ceramic board. The resulting devices were prone to fail from corroded contacts, or mechanical loosening of the connections. Early premium marine radios, especially from Marconi, sometimes used welded copper in the bus-bar circuits, but this was expensive. The crucial invention was to apply soldering to electrical assembly. In soldering, an alloy of tin and lead (and/or other metals), known as solder, is melted and adheres to other, nonmolten metals, such as copper or tinned steel. Solder makes a strong electrical and mechanical connection.