Screen Mode Mesh Plate?

jlsem · 29th June 2009, 05:06 PM

This amp is described as using the screen as the anode in triode. However the screen of the PL519 is called a "mesh". Does anyone know if the screen of a PL519 is constructed as a mesh or is it a conventional grid?

http://www.oswaldsmillaudio.com/Products/amps.html

John

HollowState · 29th June 2009, 06:28 PM

I believe that OMA is using the term "mesh" very loosely to convey the idea of an open element as opposed to solid. I know of no tube, even in the transmitting/industrial world, that has a true mesh screen in keeping with proper definition. A mesh plate yes, and a mesh filament yes. But not a screen. Someine correct me if I'm wrong.

I also think this is a waste of a good tube. A design philosophy to be different for the sake of originality and marketing hype. The same results could be obtained with a much cheaper tube. But perhaps not as "cool" looking.

jlsem · 29th June 2009, 07:25 PM

I believe that most if not all planar tubes have mesh elements (screens and control grids), but, yes, I wasn't aware of any concentrically constructed tubes that have mesh screens or control grids, other than the 849 and 851.

Quote:

I also think this is a waste of a good tube. A design philosophy to be different for the sake of originality and marketing hype. The same results could be obtained with a much cheaper tube. But perhaps not as "cool" looking.

Judging from their other projects, I don't think OMA would ever release anything that didn't work particularly well. Using the word mesh maybe a low grade of marketing hype, but I don't think the device itself was marketing-hype borne.

John

Merlinb · 30th June 2009, 01:47 PM

Looks like a convenient way of using a cheap/unpopular valve and avoiding the use of the top-cap, for a safer design.

tomchr · 1st July 2009, 12:55 AM

Well... The PL519 is a pentode, thus, would have two grids - a suppressor grid and a screen grid. It's not clear which one of the grids OMA uses as the anode in their "newly born triode". As far as I know either grid is usually quite small in area - especially the suppressor as it's only job is to catch secondary electrons knocked off the anode due to impact ionization. Using any of the grids as an anode strikes me as risky business, though. I can't imagine that they can handle much power dissipation...

I still think they should have gone with some nice turned walnut for the anode caps instead of those tire valve stem caps... :-p

~ Tom

jlsem · 1st July 2009, 04:46 AM

I doubt the suppressor grid is used because it can only handle 30V while the screen can safely dissipate 7W.

John

29th June 2009, 05:06 PM	#1
jlsem diyAudio Member Join Date: Jun 2003 Location: Dallas,TX	Screen Mode Mesh Plate? This amp is described as using the screen as the anode in triode. However the screen of the PL519 is called a "mesh". Does anyone know if the screen of a PL519 is constructed as a mesh or is it a conventional grid? http://www.oswaldsmillaudio.com/Products/amps.html John

29th June 2009, 06:28 PM	#2
HollowState diyAudio Member Join Date: Aug 2006 Location: Taxland, New Jersey	I believe that OMA is using the term "mesh" very loosely to convey the idea of an open element as opposed to solid. I know of no tube, even in the transmitting/industrial world, that has a true mesh screen in keeping with proper definition. A mesh plate yes, and a mesh filament yes. But not a screen. Someine correct me if I'm wrong. I also think this is a waste of a good tube. A design philosophy to be different for the sake of originality and marketing hype. The same results could be obtained with a much cheaper tube. But perhaps not as "cool" looking. __________________ "The supercomputer is technologically impossible. It would take all of the water that flows over Niagara Falls to cool the heat generated by the number of vacuum tubes required." ~ Professor of Electrical Engineering, New York University

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30th June 2009, 01:47 PM	#4
Merlinb diyAudio Member Join Date: May 2006 Location: York	Looks like a convenient way of using a cheap/unpopular valve and avoiding the use of the top-cap, for a safer design.

1st July 2009, 12:55 AM	#5
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	Well... The PL519 is a pentode, thus, would have two grids - a suppressor grid and a screen grid. It's not clear which one of the grids OMA uses as the anode in their "newly born triode". As far as I know either grid is usually quite small in area - especially the suppressor as it's only job is to catch secondary electrons knocked off the anode due to impact ionization. Using any of the grids as an anode strikes me as risky business, though. I can't imagine that they can handle much power dissipation... I still think they should have gone with some nice turned walnut for the anode caps instead of those tire valve stem caps... :-p ~ Tom

1st July 2009, 04:46 AM	#6
jlsem diyAudio Member Join Date: Jun 2003 Location: Dallas,TX	I doubt the suppressor grid is used because it can only handle 30V while the screen can safely dissipate 7W. John

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