stefannz":1yz94ru8 said:
Hi Guy's, Can anyone accurately tell me the sound quailty differences between
KT88's
6550...(and are they exactly the same as a KT88 ?)
EL34's
6L6's
as Diezel and other Amplifer Manufacturer's handle all of the above output valves,and why would they offer a wide range of choice ?
6L6 : Warm and balanced sound with thick, deatailed midrange, formerly the tube that North American amps were designed around. 6L6's have been around with many variants since WW2, though the originals have low power handling and metal casing. The metal ones sound horrible. KT66 is a British variant, and has a sound that's a little closer to an EL34. The ones that you want will be KT66, 5881, (Formerly an industrial variant of the 6L6GC) or the final incarnation of the tube 6L6GT. --They tend to distort later than EL-34's.
EL34: British/European tube design from the early 50's. They have a bright, deatailed crunchy sound with pronounced smooth upper midrange response. They tend to distort earlier than 6L6's, but also had greater power output than 50's 6L6 designs. Formerly the tube that was the chioce of British/European designers as they were very common in Europe. Easily spotted because the bottle design was tall and thin. There was a North American variant designated 6CA7. 6CA7's had a somewhat stiffer response and a touch less midrage crunch than EL34's. Many British amps were retofitted with 6CA7's in North America by end users due to the fact that they were a but more robust than EL34's in Ultralinear amp designs. They were a drop in replacement. True 6CA7's look much like 6L6's except for the fact that they utilise the full octal pinset, while 6L6's do not. KT77 was a variant developed by GEC, and manufactured by MO. The KT77 is slightly differant than the EL34 in the fact that it's a Kinkless Tetrode design like a 6L6, instead of a Pentode design like an EL34, otherwise it's essentially a drop in repacement for EL34 amps. --I'm unsure if current KT77 productions are true KT designs, or marketing hype. Sombody clarify?
6550: Originals were developed for the US Military in the early 50's. They were capable of handling greater plate voltages than 6L6 and EL34 designs, and therefore capable of greater power output. They were used by Marshall Amplification's American distributor in 1974 when they deemed the EL34's to be too problematic. They have a bright clean even response with very tightly controlled bass. With minor modification of the bias circuit on many amp designs they are a drop in replacement for EL34's. Because of the fact that 6550's are capable of much greater output than 6L6 and EL34's, they essentially are running de-rated in nearly all amps designed to accept 6L6 and EL34 designs. This not only increases the life of the tubes, but also creates much greater headroom response before distorting. Decent tubes for anything sources requiring loud and clean response, like bass, keyboards, or incredibly loud electric guitar. 6550 loaded Marshall amps were the sound of early 80's LA Hair metal. 6550's were also common in Sunn amps and all but the earliest Ampeg SVT's. 6550's are noticeably bigger tubes than 6L6 and EL34 tubes, and have a metal baseplate.
KT88: This was an English Upgrade to the 6550. GEC and MO took the 6550 pentode design and turned it into a Kinkless Tetrode design. I'm actually NOT familiar with these, though I've heard that they have a nicer, warmer sound than 6550's. I know that Marshall, Sound City and Hiwatt were designing amps that yeilded 200 watts from a quad of KT88's, and any British amps that could output greater than that all utilised KT88's. Furthermore, some of the Marshall amps 'Park' variants utilised a pair of KT88's and output 75 watts . Also, I'm unsure if current production KT88's are merely relabled 6550's, or vice versa, as a lot of the current production tubes are all share the same bottle and metal baseplate. --Anybody care to clarify this further?
That being said, Diezel and a few other manufacturers utilise a bias circuit that will accept all of these tubes, because of the diferrances in tonality and headroom between the above listed tubes. It's a matter of tonal flexibility.
