Editing Point-to-point construction (section)

== Terminal strip construction ==
{{redirect|Terminal strip|strips of screw terminals|Screw terminal#Multiway versions}}
<!-- Would this be better titled "Open-chassis construction"? -->
[[Image:Point to point construction.jpg|thumb|250px|Point-to-point construction of military radio equipment]]
[[File:Point to point wiring.jpg|thumb|right|Point to point wiring on a homemade tube amplifier circuit.]]
Terminal strip construction, which is often referred to as point-to-point construction within the tube guitar amplifier community, uses '''terminal strips''' (also called "tag boards"). A terminal strip has stamped tin-plated copper terminals, each with a hole through which wire ends could be pushed, fitted on an [[Electrical insulation|insulating]] strip, usually made of a cheap, heat-resistant material such as synthetic-resin bonded paper ([[FR-2]]), or [[bakelite]] reinforced with cotton. The insulator has an integral mounting bracket, sometimes electrically connected to one or more of the stamped loops to ground them to the chassis.

The [[chassis]] was constructed first, from [[sheet metal]] or [[wood]]. Insulated [[terminal (electronics)|terminal]] strips were then [[rivet]]ed, [[nail (engineering)|nail]]ed or [[screw]]ed to the underside or interior of the chassis. [[Transformer]]s, large [[capacitor]]s, [[tube socket]]s and other large components were mounted to the top of the chassis. Their wires were led through holes to the underside or interior. The ends of lengths of wire or wire-ended components such as capacitors and resistors were pushed through the terminals, and usually looped and twisted. When all wires to be connected had been fitted to the terminal, they were soldered together (and to the terminal).

Professional electronics assemblers used to operate from books of [[photograph]]s and follow an exact assembly sequence to ensure that they did not miss any components. This process is [[labour (economics)|labor]]-intensive, subject to error and not suitable for automated production. Even after the introduction of printed circuit boards, it did not require laying out and manufacturing circuit boards.

Point-to-point and terminal strip construction continued to be used for some [[vacuum tube]] equipment even after the introduction of printed circuit boards. The heat of the tubes can degrade the circuit boards and cause them to become brittle and break. Circuit board degradation is often seen on inexpensive tube radios produced in the 1960s, especially around the hot output and rectifier tubes. American manufacturer [[Zenith Electronics Corporation|Zenith]] continued to use point-to-point wiring in its tube-based television sets until the early 1970s.

Some [[audiophile]] equipment, such as amplifiers, continues to be point-to-point wired using terminal pins,<ref>[http://www.musicradar.com/news/guitars/handwired-vs-pcb-amps-whats-the-difference-633137 musicradar.com]</ref> often in very small quantities. In this application modern point-to-point wiring is often used as a [[marketing]] design feature rather than a result of the economics of very-small-scale production.

Sometimes true point-to-point wiring—without terminal strips—with very short connections, is still used at very high [[Radio frequency|radio frequencies]] (in the [[gigahertz]] range) to minimise [[stray capacitance]] and [[inductance]]; the capacitance between a circuit-board trace and some other conductor, and the inductance of a short track, become significant or dominant at high frequencies. In some cases careful PCB layout on a substrate with good high-frequency properties (e.g., ceramic) is sufficient. An example of this design is illustrated in an application note describing an [[avalanche transistor]]-based generator of pulses with risetime of a fraction of a nanosecond; the (few) critical components are connected directly to each other and to the output connector with the shortest possible leads.<ref>[http://www.linear.com/docs/4138 Linear Technology AN47 - High Speed Amplifier Techniques], p.AN47-94, figure D3, head of avalanche pulse generator. "Lead lengths ... should be experimented with to get best output pulse purity."</ref>

Particularly in complex equipment, wired circuits are often laid out as a "ladder" of side-by-side components, which need connecting to ladders or components by wire links. A good layout minimizes such links and wiring complexity, often approaching that of direct point-to-point. Amongst complex devices, the pre-PCB [[Tektronix]] vacuum-tube [[oscilloscope]]s stand out for their very well-designed point-to-point wiring.<ref>[http://w140.com/tekwiki/wiki/File:310A_foldoff.jpg Illustration of interior of Tektronix 310A oscilloscope], with complex point-to-point wiring using ceramic, rather than bonded-paper, terminal strips.</ref>

If parasitic effects are significant, point-to-point and terminal strip wiring have variable parasitic components, while the inductance and capacitance due to a PCB are the same for all samples and can be compensated for reliably which may be essential for some RF circuits. In some heavily optimised point-to-point RF constructions the circuit can be tuned by bending wires around.

Placing the completed unit in an [[Enclosure (electrical)|enclosure]] protects the circuit from its environment, and users from electrical hazards.

A few large brand names still use terminal strip-type point-to-point boards, but usually for special product lines. Electric [[guitar amplifier]] manufacturer [[Marshall Amplification|Marshall]] have reissued some of their older models, using this type of construction as a design feature, although their standard products have long used PCBs. Thermionic valve equipment usually does not have the valves mounted on the PCB in order to avoid heat damage, but instead use PCBs for the wiring, achieving the economy of mass-produced PCBs without the heat damage.