The type 27 vacuum tube was a general-purpose triode announced in April, 1927 by the Radio Corporation of America (today’s RCA). It, along with the type 24A tetrode tube, was a departure from the filament-type of tubes then in general use. Alternating current (AC) was becoming the preferred method of powering radios, and radio engineers’ new designs required tubes that could be lit from AC.

The 27 was immediately popular with both manufacturers and experimenters. It could be used as a radio- or audio-frequency amplifier, an oscillator, or a detector. The 27 gave solid, stable performance in all those applications. Consumer radios used the 27 extensively until around 1932, and the introduction of the improved type 56 triode.

Some radios, such as RCA’s Radiola 60, used only 27s for all functions except for the final amplifier tube, a type 71A. I have a Radiola 60 in my collection and it is an excellent-sounding radio, even by today’s standards.

In appearance, the first production 27s resembled old-style light bulbs. In later years, the bulb’s shape took on the more familiar “ST” shape, also known as the “coke-bottle” shape.

With the advent of glass audio (high-end amplifier employing only tubes), the 27 has made a small comeback. It was a high-production tube, and remains relatively easy to find today – on eBay, for example.


John W. Stokes, 70 Years of Radio Tubes and Valves: New York, The Vestal Press, 1982
Gerald F. W. Tyne, Saga of the Vacuum Tube, Second Edition: Indianapolis, Sams Publishing, 1987
Personal knowledge

Robert Johnson, blues legend who died in 1938, was 27 when he passed away. Legend has it he had sold his soul to the devil to be able to play the guitar.

Jimi Hendrix, electric-guitar god, died in 1970 after claiming his throne as rock's premiere rock guitarist. He was also 27 when he died. Are you experienced?

Janis Joplin, known for her raspy yet unexpectedly talented and pleasant voice, a girl who "sang the blues," died the same year, 1970, as her contemporary musician Jimi Hendrix. She was 27 at her time of death.

Jim Morrison, lead vocalist and lyricist of rock band The Doors and also well-respected for his poetry, died in 1971 in Paris. Jim was 27 when he broke "on through to the other side."

Kurt Cobain, the manic-depressive lead singer of the great Nirvana, died in 1994 after a gun-shot to the chin. He also was 27 when he passed.

Five of the most influential musicians of the twentieth century all died at the age of 27. Five who lived fast, died young, and left good-looking corpses. Five musical greats who left a legacy of musical creativity and ingenuity and who will forever be remembered. Five who found their place among the legends of music. Five who will forever be 27.

Coincidence? I think not.

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