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Advantage of beam triode over simple triode

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jan.didden

jan.didden

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Joined 2002
linearaudio.net
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#1
I am using 6HS5 beam triodes in my high voltage amplifier.
As suggested in the data sheet, I connected the beam plates to the cathode (see 'Characteristics and Typical Operation' section).
There is surprisingly little info on the 'net as to what the advantage is of a beam triode over a 'normal' triode in terms of performance.
Does it make it more linear?
I haven't been able to find a data sheet with curves.

Jan
 

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#2
platecurves-datasheet.JPG


From the vinylsavor blog. Mu of 300!
 
#4
I guess it has something to do with extreme transconductance of this tube. There is a limit to how close control grid can be placed to cathode. Not just technological problem of uniform tight spacing, but also grid emission due to grid heating by very proximal cathode. Concentrating electrons in beams allows better control by grid, translating into higher transconductance with the same k-g spacing, compared to the situation where electrons are not concentrated. So, beam-forming electrodes may play quite different role here compared to that in power beam tetrodes.

If not secret, what is your high voltage amplifier intended for?
 
#6
sser2 said:
I guess it has something to do with extreme transconductance of this tube. There is a limit to how close control grid can be placed to cathode. Not just technological problem of uniform tight spacing, but also grid emission due to grid heating by very proximal cathode. Concentrating electrons in beams allows better control by grid, translating into higher transconductance with the same k-g spacing, compared to the situation where electrons are not concentrated. So, beam-forming electrodes may play quite different role here compared to that in power beam tetrodes.

If not secret, what is your high voltage amplifier intended for?
Click to expand...
No secret, it's a direct drive amp for the QUAD ESL 63/988/989 family.

So it is a matter of higher transconductance only or does it also have an impact on the linearity?

Jan
 
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#8
There is a lot of documentation, historically, available on beam power tubes where the beam electrode is connected to (a fraction of) B+, for reasons of lowering distortion, increasing power, or both.

But so far I haven't been able to find something on a setup with the beam electrodes connected to the cathode, as in the 6HS5 data sheet I posted above.
The beam triode seems a rare bird indeed.
If you look for instance at the Sylvania GP-5, that shows a data sheet circuit with a cathode, grid and anode but is advertisd as a beam triode, so the beam plates apparently are internally connected. To the cathode?

Jan
 
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#9
One thing's for sure, you're going to have to draw your own plate curves. The factory curves for the intended pulse operation are only sketched in with a French curve in the region where you'll be wanting to operate, and can be assumed to be totally fiction. I'm guessing that you want to idle at 1kV (minimum) meaning 30mA (maximum). Is this enough (with a single valve) to slew the delay line's effective input capacitance, or will you need to parallel several? I've never seen the C number printed.

All good fortune,
Chris
 
#11
The European version is the ED500/PD500 ( and 510). It's known as a ballast triode.
There is a screen inside, not a deflection plate, i think that is to keep the electric feeld near the grid/cathode to a reasoable level. Without the screen you need a very high negative voltage on the grid to stop the electrons.Now only -15V for cut-off. Ones the triode function is done the electrons are accelerated to the anode.
But the 6HS5 is a different tube, perhaps doesn't function the same.
Mona
 
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#13
I think beam triode is not more linear than regular triode. The plate curves are just typical triode curves. There is no analogy to beam tetrode, in which beam principle creates virtual third grid to improve linearity. In beam triode it is solely to increase transconductance.
 
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#15
jean-paul said:
This was written and explained in detail many many times in magazines, technical books etc. but as often old technology theory tends to be forgotten/discarded when it is not current anymore and only the keywords stick.
Click to expand...
Do you have a reference to where beam TRIODE is explained? We all know about tetrodes, but the principle of virtual third grid does not apply to triode, as there is no screen.
 
#16
sser2 said:
I think beam triode is not more linear than regular triode. The plate curves are just typical triode curves. There is no analogy to beam tetrode, in which beam principle creates virtual third grid to improve linearity. In beam triode it is solely to increase transconductance.
Click to expand...
That could make sense as the transconductance is huge. I'll research that point further, thanks.

Jan
 
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#19
I believe:
The reason for that high voltage regulator tube was . . .
To keep the high voltage to the CRT anode below a certain value, relative to the CRT's X-ray output.
The higher the voltage, the harder the X-rays are.

Linearity was not the issue, the regulated voltage was the issue.

Use that regulator tube as a linear/non-linear gain stage at your own risk.

Just my opinions
 
#20
The high voltage was regulated to avoid screen bloom if the bruilliance would be turned up.
Changes of brilliance change the hv current, and if it is unregulated, the hv drops which increases the picture size.
You want to keep the picture size from changing, you need to stabilize the high voltage.

Jan
 
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