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Old 21st Nov 2017, 6:38 pm   #1
bigfathairyvika
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Default What is meant by "kinkless"?

Ok, I have searched google far and wide and the only answers I have found are:

a) A kinkless valve is a beam tetrode.
b ) A beam tetrode is kinkless
c) KT means Kinkless tetrode.
d) kinkless means it is kinkless.

And none of those answer the question.
My only idea is that a valve that is kinkless doesnt have a "kink" in its grid vs anode graph.
But I havent seen any valves so far that do have a kink!

This is driving me nuts...

Mark
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Old 21st Nov 2017, 6:42 pm   #2
Dave Moll
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Default Re: What is meant by "kinkless"?

I'm not the expert here, but from what I know your "idea" is about right. The plot of anode versus grid of a standard tetrode does indeed have a kink in it, and the beam tetrode was designed to remove that kink.
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Old 21st Nov 2017, 6:55 pm   #3
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Default Re: What is meant by "kinkless"?

Look at the valve characteristic curves for a tetrode, then a beam tetrode.

Lawrence.
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Old 21st Nov 2017, 6:57 pm   #4
bigfathairyvika
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Default Re: What is meant by "kinkless"?

Arh!
Right...
I can see now, pretty much all the tetrodes I have been using are beam tetrodes so I havent seen the "kink".

A bit more searching and I managed to find one with a kink.

But it does appear that the kink is only at low voltages and outside normal usage.

Mark
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Old 21st Nov 2017, 6:58 pm   #5
TonyDuell
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Default Re: What is meant by "kinkless"?

That's what I understand too. If you plot the Ia (Anode current) against Va (Anode voltage) curver for a normal tetrode, there is a region (due to secondary emission of electrons from the anode being collected on the screen grid) where the anode current decreases as the anode voltage increases -- a negative resistance region. It's possible to use that effect to make an oscillator. There is thus a noticeable kink in that graph

The kinkless tetrode/beam tetrode (and indeed the pentode) do not have this negative resistance 'kink'
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Old 21st Nov 2017, 6:59 pm   #6
bluepilot
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Default Re: What is meant by "kinkless"?

Quote:
Originally Posted by Dave Moll View Post
the beam tetrode was designed to remove that kink.
I'm not so sure about that. I thought the beam tetrode was designed to circumvent the patents on pentodes. I think it was initially the pentode that removed the kink in the characteristic. But normal tetrodes have kinks in the characteristic curve.
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Old 21st Nov 2017, 7:04 pm   #7
Synchrodyne
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Default Re: What is meant by "kinkless"?

This article might be helpful:

https://www.radiomuseum.org/forum/be...r_tetrode.html

It does include graphs that show the normal tetrode “kink”.

I understand that the name “kinkless tetrode” was coined by Osram, who then used the “KT” prefix for its valves of this type, of which the KT66 is probably best known.

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Old 21st Nov 2017, 7:08 pm   #8
bigfathairyvika
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Default Re: What is meant by "kinkless"?

It also appears that not all tetrodes are kinky.

Unless the data sheet is hiding it.
Eg: 6ER5 but it does say it is a "frame grid tetrode" so maybe not a "pure" tetrode.

And I thought solid state got complicated.

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Old 21st Nov 2017, 7:20 pm   #9
frankmcvey
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Default Re: What is meant by "kinkless"?

Wiki has a pretty good explanation here

Cheers,

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Old 21st Nov 2017, 8:37 pm   #10
PJL
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Default Re: What is meant by "kinkless"?

MS4B has a nice kink see http://www.r-type.org/pdfs/ms4b-1.pdf

This is OK for an RF valve where the signal is small but useless as an audio amplifier as you can only use less than half the ht voltage.
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Old 21st Nov 2017, 8:47 pm   #11
Dave Moll
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Default Re: What is meant by "kinkless"?

Quote:
Originally Posted by bluepilot View Post
I thought the beam tetrode was designed to circumvent the patents on pentodes. I think it was initially the pentode that removed the kink in the characteristic. But normal tetrodes have kinks in the characteristic curve.
But what I said is still true in that the beam tetrode was an alternative way to remove the kink while circumventing the patent on pentodes.
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Old 21st Nov 2017, 8:47 pm   #12
kevinaston1
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Default Re: What is meant by "kinkless"?

I believe the "kinkless" pentode was invented by Bernard Tellegen at Philips Eindhoven; memories of a Wireless World article in the 70's

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Old 21st Nov 2017, 8:58 pm   #13
paulsherwin
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Default Re: What is meant by "kinkless"?

There was a large element of marketing creativity behind these terms.
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Old 21st Nov 2017, 9:04 pm   #14
kalee20
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Default Re: What is meant by "kinkless"?

My understanding is that Walter Schottky (of Schottky diode fame in his later life) invented the suppressor grid, making the pentode!

Quote:
Originally Posted by bigfathairyvika View Post
My only idea is that a valve that is kinkless doesnt have a "kink" in its grid vs anode graph.
But I havent seen any valves so far that do have a kink!
It's actually in its anode current vs anode voltage graph, grid voltage is not really relevant except to shift things up or down.

You probably haven't seen a valve with a kink because there weren't many types made! A kink in the characteristic is rarely desirable.

But, if you get a pentode with the suppressor brought out to its own pin c(eg EF80), and instead of connecting it to cathode like normal people do, connect it to anode or screen-grid so that it just becomes part of that electrode. You may well be able to demonstrate the tetrode kink then! If you do, let us know how you got on!
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Old 21st Nov 2017, 9:11 pm   #15
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Default Re: What is meant by "kinkless"?

Quote:
Originally Posted by bigfathairyvika View Post

And none of those answer the question.
It is the opposite of 'kinky'
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Old 21st Nov 2017, 9:25 pm   #16
Synchrodyne
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Default Re: What is meant by "kinkless"?

The 6ER5 was in fact a frame-grid VHF triode, not a tetrode, and was evidently improperly named when it was released, as explained here:

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The Mazda 30F27 was a frame-grid VHF tetrode. It had aligned grids and possibly followed the Harries principle in order to minimize the incidence of kinking. I haven’t seen the curves for it though. I think that Sylvania also had a double VHF tetrode (on a decar base) for FM front end applications. Here is the background to the Harries valve:

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The above-mentioned Wikipedia article suggests that the Harries valve was an alternative development aimed at minimizing tetrode kink. But as I understand it, the Harries idea of a space-charge virtual suppressor grid was integral to the beam tetrode as developed by Osram, and also taken up by RCA via its information exchange pathway with Marconi.

In the RMorg article, the “side-plates” commonly used in beam tetrodes are referred to both as “beam-confining plates” and “beam-forming plates”. The first is more accurate, I think. The sheet beams are formed by valve geometry, namely grid spacing and alignment of the screen and control grids, and do not require the presence of the side plates. Rather their function is to keep the sheet beams away from those parts of the valve, where due to the presence of support rods, changing geometry at the ends of elliptical long axes, etc., the low-potential virtual suppressor grid is less well-defined.


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Old 21st Nov 2017, 11:33 pm   #17
turretslug
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Default Re: What is meant by "kinkless"?

Quote:
Originally Posted by paulsherwin View Post
There was a large element of marketing creativity behind these terms.
I've long suspected that marketing was behind the designations of the KTW61 and KTW63- on circuit diagrams, they are invariably shown as pentodes and, as far as can be made out through the inner-coated glass, they are indeed constructed as such. If I could bring myself to sacrifice one....(and they are pretty common, after all). The W61 is listed as an "equivalent" of the KTW61- it would be interesting to closely compare the electrode structures of these two, they might be very similar indeed!

Perhaps the success of the KT61, 63, 66 etc. (and the latter in particular) led M-O V to feel that "KT" had become enough of a symbol of success that it was now almost a brand in its own right and was applied to valves where it was not strictly technically relevant. Pressed on the issue, a company spokesman might have responded that a pentode was indeed a form of kinkless tetrode, though such an argument would hold more water in the case of valves with internal suppressor-cathode connection- the small-signal "W" types having separate cathode and suppressor pins.

Which reminds me- the 6F6 (a pentode) is quoted as equivalent to the KT63, perhaps the latter is also a pentode. Another case of sacrificial duffer required.
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Old 21st Nov 2017, 11:39 pm   #18
kalee20
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Default Re: What is meant by "kinkless"?

And the EL37 is often quoted as equivalent to the KT66, although the former is a pentode and the latter a beam tetrode!
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Old 22nd Nov 2017, 12:03 am   #19
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Default Re: What is meant by "kinkless"?

It went something like this..

the triode was a useful valve with some good properties, but against it was the action of the stray capacitance from anode to grid creating feedback and reducing the gain.

So to solve this, someone put a second grid around the first one. This grid was decoupled to chassis so it had no signal on it. We got some g1 to g2 capacitance and anode to g2 capacitance, but very little of the more damaging anode to g1 capacitance.

This was now a much higher gain bottle. But the screen grid had to be biased at a high positive voltage else it reduced the current too much. Then when the anode voltage dipped below the screen voltage, anode current would switch from the anode and flow to the screen grid instead. The screen grid being more positive than the anode had become a much more tempting target for the negatively charged electrons. This made the famous kink. in the anode current at lower anode voltages. The valve was useless for any application needing a wide voltage swing.

So manufacturers sought ways of fixing the kink with various electron ballistics tricks. While the engineers were doing this, the marketing departments were making all sorts of claims, coining trade-names and sowing a lot of disinformation and scuttlebutt about competitors. It is now somewhat uncertain who did what and why. The waters were muddied so much we still get confused by it all. Patents and lawsuit were whizzing around.

David
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Old 22nd Nov 2017, 1:14 am   #20
bigfathairyvika
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Default Re: What is meant by "kinkless"?

Just spent a few hours in the loft looking for and found a box of EF80's.
Tomorrows task is to observe a kink.

Thanks everyone for the replies.

Mark
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