[1] The EL34 has an octal base (indicated by the '3' in the part number) and is found mainly in the final output stages of audio amplification circuits; it was also designed to be suitable as a series regulator by virtue of its high permissible voltage between heater and cathode and other parameters.

One application of this type was in "Australian Sound" public address amplifiers commonly used in government schools in Australia in the 1950s, using four EL34s for ≈200 watts.

However, Sylvania (and possibly GE) marketed a tube as 6CA7 which was not only in a markedly different 'fat boy' envelope, but used a beam forming plate much like a 6L6.

Some firms make a related tube called an E34L which is rated to require a higher grid bias voltage, but which may be interchangeable in some equipment.

The EL34 was widely used in higher-powered audio amplifiers of the 1960s and 1970s, such as the popular Dynaco Stereo 70 and the Leak TL25 (mono) and Stereo 60, and is also widely used in high-end guitar amplifiers because it is characterized by greater distortion (considered desirable in this application) at lower power than other octal tubes[citation needed] such as 6L6, KT88, or 6550.