One of the most popular power tubes of all was originally intended as a cheap way of getting 40 watts, with high sensitivity. The purpose was to allow amplifier designers to make a driver/phase splitter with the minimum components count. Low distortion was incidental, as this tube was to be used in a push-pull pair with negative feedback, and other applications (such as radio transmitters) were not even really addressed. Although beam-power tetrodes had taken over the market in the 1940s, this new tube was a true pentode, an archaic design by the standards of the day. This may have been done in order to circumvent RCA's patents on beam tubes. Strange as all this must have seemed, Mullard took just this big leap when they introduced the EL34 in late 1953.

In spite of the low-cost intent, the early EL34 was an excellent tube. The Mullard early version (recognizable by the metal ring around its base) could defeat any 6L6 easily, and was almost a match for the 6550. It gave easy drive and considerable peak power, from a tall and thin glass envelope that saved space on chassis. Mullard's book CIRCUITS FOR AUDIO AMPLIFIERS, first published in 1959 and recently reprinted by Audio Amateur Publications, featured the EL34 in the largest power-output design. All the other amps in that book used the much smaller EL84 or ECL82.

Among the first amps to use it were the Marantz 2 (1955), Dynaco Mark II, and the Pye Mozart, a single-ended 9-watt British unit from 1956. The easy drive requirements allowed a 30-40 watt amp to be built using only 3 tubes: the two EL34s, and a triode-pentode as the voltage amp and phase splitter. This made the EL34 a must for Dynaco to use in their Mark II and its low-cost stereo version, the Stereo-70. At least half a million Stereo-70s were sold from 1958 to 1977. The EL34 is also found in the Marantz 5, 8A, 8B and 9; the H. H. Scott 240, 250 and 290; the Eico HF60 and HF87; the Heath W-7A; the Acrosound UL-120; the Fisher X-1000; and many, many others. These are some of the best tube hi-fi amplifiers ever made, all using "a cheap way of getting 40 watts". So it wasn't such a bad tube after all. And in fact, many audiophiles prefer it over the 6550 and other types.

The EL34's popularity was sealed when Jim Marshall selected it for his JTM45 guitar amp in 1965. He went with it because it was cheaper and easier to get in England than the 6L6 he had used previously. That amp became a standard for the British blues-rock sound. The EL34 also found its way into Hiwatt, Orange, Traynor and Laney amps, all made in Britain. Because the EL34 has a much more pronounced distortion characteristic than the 6550 or other similar power tubes, its sound is distinctive and is a major influence on the heavy rock sound palette. Marshalls are often run full-tilt, which has caused reliability problems. In fact, the American importer of Marshalls was putting more-rugged 6550s in the amps during the late 1970s and early 80s. But when new distribution was set up in 1986, Marshall was adamant that the amps be equipped with EL34s exclusively.

Why do EL34s sound so different from other tubes in guitar use? Because they were low in cost, they had a less "hard" vacuum and a less rigid structure than 6550s and similar types. Since the signal voltages in a tube amp can get very high at times, the tube's piezoelectric and mechanical behavior can influence the sound. Overall, most EL34s have a softer distortion tone than 6L6s or 6550s because of the construction differences and the pentode design. The so-called 'STRs' and KT77 are actually beam types and tend toward more "hard" quality. This is usually not easy to hear at low volumes, but is quite apparent when the amp is pushed into clipping distortion, especially in a guitar amp. So personal preference can be a major factor.

2. Versions
No power tube can compare with the 6L6 for sheer number of variations, but the EL34 was quite popular, and thus many EL34s and EL34-likes have been marketed over the years. This is still true, with five (soon to be six) versions currently being manufactured in 1995.

But the perfectionists still look to NOS versions for the standards. Mullard made three major editions, all quite different but all of very good quality. The first we have already mentioned: the metal-base version, called the "Type I". The base ring is actually a cheap stamping of nickel-plated steel. The tube inside it is one of the best; original Mullard data sheets give maximum voltage ratings of 650 for the plate, 500 for the screen. Dissipation has always been listed at 25 watts, but could usually be exceeded (and often was in certain guitar amps). This may seem unlikely, but well-used Type Is often have heat-stress cracks in the metal ring yet can still test like new. The Type II had a large base of dark-brown bakelite, but was quite similar in other respects to the Type I. This version appeared around 1959. It is often seen relabeled 6CA7/EL34, with RCA, GE or Sylvania logos. (The American JEDEC designation 6CA7 apparently was bestowed around 1960.) It's also the original tube seen in 60s Dynaco amps, with the Dynaco brand. All the Mullards can be recognized by a pair of 4-digit production codes imprinted on the glass with a permanent paint. The Type I and II had crimped plates with two rectangular holes on either side, the classic profile.

The Type III appeared about 1968-69. Its base was smaller and black, with a similar structure inside. There were three variations of the Type III: first with two getter "haloes", then with one, and finally (in the 1980s) with one halo and a spot-welded plate. Experts on them say that Mullard's quality started to slip in the 1980s, and the welded plate EL34s were the least consistent of all, had screen-dissipation problems, and ended up being the last true Mullards. The plant was shut down in 1988. Since Philips owned Mullard, some Philips and Norelco EL34s were actually made by Mullard (see Amperex below).