The 6L6 Beam Power Tetrode: An All-American Tube?

Made famous for its use as the output tube of the famed 1965 Fender Twin Reverb guitar amp, does the 6L6 beam tetrode really claim the fame as an all-American tube?


By: Ringo Bones


As the guitar amp that many electric guitar players view as the “soul-mate” of Leo Fender’s late 1950s iconic invention – the single-coil pickup equipped Fender Stratocaster – the 1965 Fender Twin Reverb guitar amplifier has over the years managed to inexorably sneak itself into posterity. But given the venerable guitar amp’s claim to fame of being as American as apple pie and baseball, does the output power tubes that made the 1965 Fender Twin possible – namely the 6L6 beam tetrode power tube – really claim the fame as an all-American tube? But first, let us examine this remarkable vacuum tube’s – or valve as they say in merry old England – history.

A guy called Schottky originally invented the screen grid-type tubes / valves called tetrodes while working for Siemens of Germany during the 1930s. Schottky’s work with tetrode-type tubes eventually lead to the creation of the 6L6 beam power tetrode and the KT66 tube. The 6L6GC tube was first introduced in1936 for a new generation of audio power amplifiers that produced high gain and lower total harmonic distortion with the help of the newly discovered principle of negative feedback. Amplifiers using the 6L6 tube became so popular over the years that it was eventually used in the 1965 Fender twin Reverb guitar amplifier that produces an 85-watt output using an all-tube driver stage. Often equipped with 12AX7 pre-amp tubes for the input stage and phase splitting duties and a12AT7 pre-amp tubes to drive the spring reverb section of the guitar amp.

As major American consumer electronic manufacturing firms made the shift from using vacuum tubes to solid state components like transistors and integrated circuits or ICs - which were reaching the point of becoming cheaper to manufacture than their thermionic counterparts. American audiophiles and electric guitar players who are still reliant on tube-based gear were left high and dry when it comes to acquiring replacement tubes. Some went to buying new old stock (NOS) US manufactured tubes, only to find out that these items slowly crept up in price as the years went by despite of their reliability and wide availability. Especially during the 1980s where everyone in the US seems to be starting their very own Heavy metal band, and you know how this kind of music is very reliant on tube-based electric guitar amplifiers when it comes to getting a good tone and feel.

Eastern Block countries during the eve of the fall of the Iron Curtain became a very important source of vacuum tubes for electric guitar and PA amplifier use almost overnight. Unfortunately, Eastern Block tube manufacturers – especially in China and Yugoslavia – still have a very steep learning curve to conquer in order to produce vacuum tubes that would equal the reliability and sound quality of American made tubes. It was only during the mid 1990s that Russian made tubes finally equaled their American NOS counterparts and China – and other Eastern European countries – had to wait till the very late 1990s or early 21st Century for their tubes to equal American made ones.

Those of us who don’t have more money than our common sense and/or were born a few years after Neil Armstrong and Buzz Aldrin walked on the Moon. It will be very unlikely that we’ll be using ultra-expensive American NOS versions of the 6L6 beam power tetrode tubes on our 1965 Fender Twin Reverb guitar amp. It is more likely – probably 99.9% - that we’ll be using Russian Edicron 6L6GC tubes if we want for our beloved 1965 Fender Twin to sound its best. Though a Chinese made Golden Dragon 6L6 will provide a little more power if we tweak the power amp circuit so that the cathode resistor voltage readings of the 6L6 tubes will rise to about 35 volts or so with reference to ground.

So is the 6L6 beam power tetrode tube an all American tube especially when used as the output tubes of an all American guitar amp like the 1965 Fender Twin Reverb? Well, it probably depends on how you define what constitutes being American anyway. Given that the American culture has been further enriched each time Americans indulge in the niceties of newly arrived ethnic groups then yes the 6L6 tube does pass muster as an all American tube. Whether it is made in post-Soviet era Russia or the People’s Republic of China. Especially the Chinese made ones, which fortunately haven’t managed to self-destruct during the Free Tibet concert or the Chinese made 6L6 tubes on guitar amps played in a Jetsun Milarepa fundraising. This tube is as American as apple pie, baseball or just “Rockin’ in the Free World”.