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May 14, 2018

I started building electronic circuits in the final years of vacuum tube electronics. Vacuum tubes served the amplification function that is now done with transistors. The integrated circuits of today contain tens of billions of transistors, a considerable fraction of the number of stars of our Milky Way Galaxy, while a popular consumer radio receiver of the mid-20th century, the "All American Five," had just five vacuum tubes.

'All American Five' radio, circa 1947

All American Five radio receiver, circa 1947.

This Emerson AM Table Radio, Model 547A, had the following five 7-pin miniature tube complement: 35W4 (rectifier), 12BE6 (superheterodyne converter), 12BA6 (IF amplifier), 12AT6 (detector and first audio amplifier), and 50B5 (audio power amplifier).

The tube complement of earlier All American Five radios had a 35Z5 rectifier, 12SA7 superheterodyne converter, 12SK7 IF amplifier, 12SQ7 detector and first audio amplifier, and 50L6 audio power amplifier.

(Wikimedia Commons image by Joe Haupt)

Man makes good use of natural materials, and this was evident in early electronics. While cotton as wire insulation was replaced very early by polymers, the mineral, mica, has excellent dielectric properties, and it was used in capacitors into the last half of the 20th century. The particular mica used in capacitors was muscovite, a monoclinic crystal with a perfect basal cleavage that allows its separation into large, thin sheets on {001} planes. The chemical composition of muscovite is KAl2(AlSi3O10)(F,OH)2.

Mica was used in capacitors since its dielectric constant can be as high as 9.3,[1] it has an extremely high dielectric strength of ~100 V/μm, and its crystals can be huge, thereby yielding large sheets of dielectric. Since mica is composed of elements with small atomic number, it's relatively transparent to alpha particles, so it's used as a window on Geiger-Müller tubes in "Geiger" counters.

Component designers crave uniformity, so industrial materials are preferred over natural materials. In 1913, Daniel J. O'Conor, Jr. patented a mica substitute for electrical equipment manufacturer, Westinghouse.[2] This mica substitute with a dielectric constant of about four was called Formica. It was a laminate of paper or textile bonded by phenolic resin, and the Formica name derived from a combination of mica and the formaldehyde component of phenolic resin.

Formica material and Formica rufa insect

Two examples of Formica.

On the left, Formica was used by my father, a carpenter, to make me a case for an electronic music synthesizer keyboard in the 1970s. On the right, an example of Formicidae, in this case a European red wood ant, Formica rufa.

(Left image by the author. Right image, a Wikimedia Commons image by Richard Bartz.)

While his patent presented a more conventional method of sheet lamination, O'Conor devised a more efficient method of forming this Formica composite material. Fabric was coated with resin as it was wound on a spindle, the roll was slit lengthwise to yield a curved sheet, and this sheet was pressed flat and cured.[3] As is typical for such "work for hire" inventions, O'Conor was awarded a dollar for his invention (My employer in the 1980s gave us two dollars, an award that was later upgraded to shares of company stock).

O'Conor and a Westinghouse sales engineer, Herbert A. Faber, immediately left Westinghouse to form a company to produce this material with an initial $7,500 investment (about $200,000 in today's money).[3] This company was first named, Formica Products Company, but the name was soon changed to The Formica Insulation Company to reflect their principal product, a material for electrical insulation.[3]

Although initial production of Formica was for electrical insulation, the use of Formica for automotive timing gears was developed in the 1920s. In 1927, wood-grained and marble-textured laminates were developed for the decorative sheets that are usually associated with the Formica name.[3] In 1938, phenolic resin was replaced by the superior melamine resin. Thermosetting melamine resin, developed by American Cyanamid, was more heat, moisture, and abrasion resistant than phenolic resin, and it could take more colors.[3]

Melamine resin was invented by William F. Talbot of Monsanto Chemical Company, and it was patented in 1941.[4] Melamine is notable for its use in Melmac dinnerware prevalent through the 1970s. My wife and I were given Melmac dishes when we were married. Melmac dinnerware was prone to staining and scratching, and the added problem that they were not microwave-safe caused diminished sales. Melmac was still used for children's dinnerware, including the "My Little Pony" dinner set that my daughter had.

Portion of the patent, 'Manufacture of melamine-aldehyde condensation products,'US Patent No. 2,260,239, by William F. Talbot, October 21, 1941.

First portion of US Patent No. 2,260,239, "Manufacture of melamine-aldehyde condensation products," by William F. Talbot, October 21, 1941.

(Via Google Patents.[4])

It's interesting to examine the simplicity some of the early polymer reactions, and the melamine resin reaction is a good example. As shown below, you merely condense formaldehyde (CH2O) with melamine (C3H6N6) to form the hexa-hydroxymethyl derivative. Heating this derivative in the presence of an acid causes the crosslinking that leads to a high strength polymer.

melamine-formaldehyde reaction

Polymerization of melamine resin. Melamine is condensed with formaldehyde to form a hexa-hydroxymethyl derivative that forms the melamine resin polymer in the presence of an acid. (Wikimedia Commons image.)


  1. J. R. Weeks, Jr., "The Dielectric Constant of Mica," Phys. Rev., vol. 19, no. 4 (April 1, 1922), pp. 319ff., DOI:https://doi.org/10.1103/PhysRev.19.319.
  2. Daniel J. O'conor, Jr., "Process of making composite material," U.S. Patent No. 1,284,432, February 1, 1913.
  3. Formica history, early years, from formica.com, via archive.org.
  4. William F. Talbot, "Manufacture of melamine-aldehyde condensation products," US Patent No. 2,260,239, October 21, 1941 (via Google Patents).

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