The EL34 has traditionally been the power amp tube in tube amplifiers from European manufacturers since the 1950s. Developed and produced by Philips and Mullard, the EL34 achieved cult status in the 1960s and 1970s through its use in guitar amplifiers by Jim Marshall, Hiwatt, Laney, WEM, VOX and many more.
Variants of the EL34 are the 6CA7, the American model, and the KT77 by GEC / MO-Valve (UK) called Kinkless-Tetrode to get around Philips' patent for pentodes at these days.
Today, EL34s are still produced and used in both guitar amplifiers and hi-fi audio amplifiers. The EL34 is still synonymous with the British guitar sound shaped by the Marshall brand and guitarists Jimi Hendrix, Pete Townshend, Eric Clapton, Angus Young and many more.