Kinkless, my eye

[Enzo]

I have been in this electronics thing for well over 50 years, and have learned a lot. On the other hand, I do indeed learn something new every day. Often useful or not so useful insights. But sometimes I am amazed that some very basic item had escaped my attention all these years, and then there it is. But I like to think I have a reasonable idea what is real and what is imagined.

For example, people hear something often enough, and they start to think it is true. Some folks hear over and over that a tube amp MUST be rebiased every time tubes are replaced. Well, I have actually had someone come to me with a Fender Champ and ask me to put a bias adjustment on it, so this advice could be followed. He wondered why Fender had made this HUGE oversight by not including this "necessary" control. (yet another example of: I don't understand something, so it must be a design flaw.)

SO what am I yammering on about? "Kinkless tetrodes." I often hear that the KT in KT-88 means "kinkless tetrode." I don't believe it for a second. Now I could be completely wrong here, but I just don't swallow it. It sounds like one of those made up after the fact sorts of stories.

COnsider, EL34 or EL84 doesn;t stand for "Extremely Lively" or anything. And ECC83 I don't think means "electronically cool compression." And EF86... "eh, ferget it..." None of the other indicators refer to actual words, or at least English words. And yet the lone KT designation is supposed to. I know the E in the above examples just means 6v heaters.

Is ther any real documentation of the history of these type numbers? The whole kinkless thing does make a compelling story, but is it really a true story. What on earth would a kinkless tube be anyway? I have been told it referred to a reduction of crossover distortion or something. Well... I don't think any tube has an inherent anti-crossover capability, that all derives from the circuits the tubes find themselves in.

What do we think?

[Chuck H]

I can't find any indication of what the KT designation might stand for other than "kink-less tetrode". Since tetrodes do "kink" I suppose the myth is more than plausable. The following article isn't kt88 specific but does explain the "tetrode kink", ergo what the advantage of a kink-less tetrode might be.

From some site:

The story starts with the screened-grid tetrode which was developed to minimise the anode to grid capacity by interposing an electrostatic screen at HF earth potential. The screen was so effective that it prevented the field from the positively charged anode from penetrating to the grid. Thus electrons passing through the grid having no anode field to act upon them went no further. The cure of course was to put a positive bias on the screen to help the electrons on their way to the anode. The resultant device was a great success, revolutionising HF amplification, but it had a serious problem: the tetrode kink, which rendered it unsuitable for large signal handling (power amplification).

The problem was caused by anode secondary emission. Any thermionic valve operating at an anode potential above 10 V emits secondary electrons from the anode as a reaction to the bombardment by primary electrons from the cathode. These secondary electrons are attracted to the most positive electrode which in the case of diodes and triodes is the anode. If all the secondary electrons emitted by the anode return to it, the net secondary emission current is zero therefore we cannot detect any effect.

In a tetrode we have a second positively biased electrode (the screen) which also attracts secondary electrons. If all the anode secondary electrons do not return to the anode, the net anode current is the number of primary electrons from the cathode minus the number of secondary electrons captured by the screen thus the anode current falls, producing the tetrode kink (see above). As the dynamic anode voltage swings down following a signal, a point is reached when the almost constant anode current begins to drop very rapidly. When the anode potential approaches the screen bias the anode current begins to drop very rapidly. When the anode potential is less than the screen bias the screen is the most positive electrode and collects virtually all the secondary electrons and since at an anode potential of 40 or 50 V these can outnumber the primary electrons, the net anode current can fall to zero and even go negative.

[Enzo]

Fair enough, at least there is a technical discusion behind that. But i am still skeptical. I see the curves there are low voltage and low current, like a radio tube or some other low power application. Yet the only KT tubes I know are modern power output tubes. What tube is that anyway?

[tubeswell]

And this:
"The KT66 was essentially a 6L6 redesigned with a larger cathode and a shorter, fatter anode. The KT66 had less rapid acceleration, longer electron paths, and almost no kink." From Here: KT66 @ The National Valve Museum

And some other site:
http://www.jacmusic.com/KT88/kt88.htm

What the hell is that kink doing in there? http://www.jacmusic.com/KT88/kt88-6g.gif

I suspect there might be something in here http://www.tubebooks.org/Books/intro_rider_inside.pdf (Ch12) but I can't be bothered downloading it today to find out

from this site: http://www.tubebooks.org/technical_b...ine.htm#Vacuum Tube theory & circuit design

I was always under the impression it stood for Kinkless Tetrode as well

[jrfrond]

As far as I always knew, it IS "Kinkless Tetrode", and I've always thought that the remedy for the tetrode kink was substituting beam plates for screen grids. I guess you can call it an assumption, because all tubes in the KT-series (66, 77, 88, and the newer 100) are beam-power tubes, roughly analogous to the 6L6, 6CA7 and 6550 American tube types respectively (100 is on it's own apparently).

I never really gave it much thought, but I DO like the track you are on with the acronyms Doug!

[Ronsonic]

Part of the problem is that KT is a proprietary brand name while EL is standard Euro-tube speak for 6V heater Power Pentode. F is a signal pentode, C is a triode, CC is a dual triode and like that. The numbers that follow are arbitrary like the letters in the American tube nomenclature.

The "kinkless" thing as I understand it, refers to the smoother curve of a beam tetrode compared to a pentode.