Photo by Tom Moberly.
- NOS electrical specs (Philips Data Handbook)
- Classification by construction: “A.F. output pentode”)
- Filament volts: 6.3 V
- Filament current: 1.5 A
- Max plate volts and watts: 800 V, 25 W
- Max screen volts and watts: 500 V, 8 W
First introduced in the early 1950s in the Netherlands, the EL34 is commonly associated with the British sound of high-gain Marshall amps. In 1966 Marshall switched from the KT66 to the EL34 as their power tube of choice. In September of that year, Jimi Hendrix arrived in England to form the Jimi Hendrix Experience and, taking his cue from Pete Townshend of the Who, began cranking Marshall amps. The EL34’s low-end frequency response is leaner and possibly meaner than that of the 6L6GC. With tight mids and crisp highs, the EL34 is more easily overdriven than the 6L6GC, providing softer crunch distortion.
A 1959 Super Lead Plexi Serial #12237—with tight mids and crisp highs, the EL34 is more easily overdriven than the 6L6GC, providing softer crunch distortion. Photo courtesy of Marshall Amplification.
The 6CA7 and KT77 are common substitutes for the EL34. The 6CA7 is the American designation for EL34, and some 6CA7 versions use beam power construction instead of a true pentode. Try a 6CA7 in place of an EL34 for more pronounced low-end frequency response with a little more headroom.
The tonal differences between the KT77 and EL34 aren’t dramatic, but there is a significant structural difference: the KT77 doesn’t have an internal connection at pin one like the EL34 and 6CA7 do. This can make it easier to install KT77s in certain American amps designed for the 6L6GC, yielding a more British sound. Amp manufacturers would often use lug 1 of the tube socket for other circuit connections incompatible with an EL34. Could this be why the MOV (Marconi-Osram Valve Co.) datasheet designates the KT77 as having an “international octal” base? If not, at least it helps us remember that there is a difference between the pinouts of the EL34 and KT77.