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New production Tung Sol 6550s

#21
They're both beam tetrodes. You can see on that GE data sheet that there's no suppressor grid and pin 8 is connected to the cathode and beam plates.

Edit: Just noticed you took that part out of your post WretchedExcess. I was trying to quote you for clarity and suddenly what I was trying to quote was gone, threw me for a loop haha
 
#23
Cutting down on the size of my previous post for the sake of being concise, Jimmy -- I honestly don't think that KT88 sound all that different from 6550, and I doubt that you'd notice a difference. Electrically, the 6550 have less of what they call "outer mu" meaning that they prefer to operate with a lower screen voltage. In an amp that's designed for a 6550 I don't think you'd notice a difference. On an amp that's designed to be ultralinear like a Marshsall Major you might get better life out of a KT88. But for an SVT, I haven't tried it, but I don't think it matters at all. Chances are that with the new production tubes that none of this really matters, and we're just clinging to the past. It wouldn't surprise me if the innards of a JJkT88 and a JJ 6550 are the same. They sure do look the same to me.
 
#24
ShrewTamer said:
Edit: Just noticed you took that part out of your post WretchedExcess. I was trying to quote you for clarity and suddenly what I was trying to quote was gone, threw me for a loop haha
Click to expand...

Sorry 'bout that. I took that part of the post down to revise it to make things easier to follow. I'll put it back:



When it comes to difference in sound, you have to consider what type of design the tube has, specifically, whether it's a pentode or a beam tetrode, or the beam pentode. This is where it can get confusing.

Tetrodes existed before pentodes, and they had a problem with a negative resistance "kink" in their plate characteristic curves. The result is that tetrodes were not reliable for audio power amplification applications. Pentodes were developed to solve this problem and the 5-electrode tube design was patented by Mullard. In turn, to circumvent paying Mullard for the right to use pentode designs, a new type of tetrode was developed, the beam tetrode. It used an additional electrode to focus the electron beam to do away with the problem with the "kink" in the tetrode's plate characteristic curve. This made it a good tube for audio frequency power amplification applications. Although it had 5 electrodes, they chose not to call it a "pentode" becuase of Mullard's patent. Instead they called it a "beam tetrode." Because the geometry of the 5th electrode was different, they circumvented Mullard's patent.

In terms of distortion, on paper the beam tetrodes are actually superior to pentodes for push-pull designs in audio frequency applications. The reason for this is that while a pentode's distortion primarily consists of 3rd harmonic and to a lesser extent 2nd harmonic, a beam tetrode's distortion primarily consists of 2nd harmonic and to a lesser extent 3rd harmonic. In a push-pull configuration the even order harmonics cancel out, such that THD is determined mostly by 3rd harmonic, which is lower for a beam tetrode then for a pentode. The bottom line then, is that a beam tetrode in push-pull is going to be a bit cleaner sounding due to less 3rd harmonic distortion, where a pentode in push-pull to have more 3rd harmonic distortion. (The increase in THD is why guitards like EL34 pentodes.)

That's the theory, anyway. Who knows what you'll get with today's production tubes.

Now all of this gets even more complicated with the advent of the 6550. The 6550 is called a "beam pentode." Actually, it's still a beam tetrode, but GE started using the "beam pentode" designation as a marketing gimmick after the Mullard patent on the pentode had expired. They were trying to play both sides of the fence, claiming that the 6550 combined the best features of a beam tetrode and a pentode. The KT88 is a classic kinkless tetrode (aka beam tetrode).

Unless you drive your amp really REALLY hard, I don't think you'll notice much difference between a 6550 and a KT88. Chances are that the JJ tubes use the same guts and only the envelope is different.


Ref: http://www.r-type.org/static/grid14.htm
 
#25
WretchedExcess said:
Cutting down on the size of my previous post for the sake of being concise, Jimmy -- I honestly don't think that KT88 sound all that different from 6550, and I doubt that you'd notice a difference. Electrically, the 6550 have less of what they call "outer mu" meaning that they prefer to operate with a lower screen voltage. In an amp that's designed for a 6550 I don't think you'd notice a difference. On an amp that's designed to be ultralinear like a Marshsall Major you might get better life out of a KT88. But for an SVT, I haven't tried it, but I don't think it matters at all. Chances are that with the new production tubes that none of this really matters, and we're just clinging to the past. It wouldn't surprise me if the innards of a JJkT88 and a JJ 6550 are the same. They sure do look the same to me.
Click to expand...
Much like the 6L6GC's and the 7027's they make, I'd suspect. Wouldn't surprise me a bit.
 

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