Several postings mention that for a triode in A2 mode, i.e. with cathode voltage below the grid voltage, the grid starts to become a second cathode leading to substantial current flowing from Anode to Grid, causing less current to arriving on the Cathode.
In that case, Ianode would be Igrid+Icathode.
However In my simulation of a GM-70 I see the opposite, where the Grid starts to become an Anode sourcing current to the cathode.
So Ianode + Igrid = Icathode.
Is my simulation model correct or not ?
Hans
In that case, Ianode would be Igrid+Icathode.
However In my simulation of a GM-70 I see the opposite, where the Grid starts to become an Anode sourcing current to the cathode.
So Ianode + Igrid = Icathode.
Is my simulation model correct or not ?
Hans
In A2 mode, the grid -partly, or completely, depend of operating point- positive compared to cathode.
It's a diode, current flowing from grid to cathode (if driver able to do that), so overall cathode current growing.
It's a diode, current flowing from grid to cathode (if driver able to do that), so overall cathode current growing.
The grid that is positive with respect to the cathode . . . causes acceleration of the electrons in the cloud to go to the grid.
But the grid is open between grid wires, so some of the Already Accelerated electrons are going to pass between the grid wires, and therefore will reach the plate even quicker . . . so you get more plate current.
A grid that is biased at say -10V with respect to the cathode, prevents the electrons in the cloud from accelerating to the grid, and the field between the grid wires prevents the electrons from being as attracted to the plate . . . so there is less plate current.
Just for fun, look up the 4X150A Beam Power Tetrode, and the construction of the bird cage g1 grid, birdcage g2 grid.
g1 and g2 are perfectly lined up.
The plate can "see" all the way back to the cathode.
The tube is often operated with a positive g1, and of course almost always with a positive g2.
So, the electrons are first accelerated to g1, then to g2, then to the plate.
Hint: the 4X150A is a True Tetrode. 4 elements . . .
Filament/cathode
g1
g2
Plate.
The 4x150A does not have a 5th element.
5th elements are only in Pentodes, and Beam Power ["tetrode"] tubes.
Confused with naming conventions?
Many are.
But the grid is open between grid wires, so some of the Already Accelerated electrons are going to pass between the grid wires, and therefore will reach the plate even quicker . . . so you get more plate current.
A grid that is biased at say -10V with respect to the cathode, prevents the electrons in the cloud from accelerating to the grid, and the field between the grid wires prevents the electrons from being as attracted to the plate . . . so there is less plate current.
Just for fun, look up the 4X150A Beam Power Tetrode, and the construction of the bird cage g1 grid, birdcage g2 grid.
g1 and g2 are perfectly lined up.
The plate can "see" all the way back to the cathode.
The tube is often operated with a positive g1, and of course almost always with a positive g2.
So, the electrons are first accelerated to g1, then to g2, then to the plate.
Hint: the 4X150A is a True Tetrode. 4 elements . . .
Filament/cathode
g1
g2
Plate.
The 4x150A does not have a 5th element.
5th elements are only in Pentodes, and Beam Power ["tetrode"] tubes.
Confused with naming conventions?
Many are.
Another way to think about it is that a positive G1 acts like G2 always does.
All good forrtune,
Chris
All good forrtune,
Chris
A Heptode is a little bit like a Sunbeam electric mixer, it blends several signals, like ingredients in a casserole.
I think the following is historically correct:
I believe Pentodes were once patented. 5 elements: filament/cathode; control grid, screen grid, Suppressor Grid, and plate.
The Suppressor grid was patented.
Other tube manufacturers needed a way around the patent of the 5 element Pentode that had a Suppressor Grid.
Aha . . . they came up with a set of beam formers . . . and the Beam Power tube was born. No need for a suppressor grid.
Pretty soon, patents ran out, names were no longer used in the historical way.
Marketing took over with "what would you like us to call it", and the confusion began.
Beam Power Tetrode, and Kinkless Tetrode . . .
Those are actually Beam Power tubes (they have beam formers); marketing just re-named them.
$0.03
Adjusted for inflation
I believe Pentodes were once patented. 5 elements: filament/cathode; control grid, screen grid, Suppressor Grid, and plate.
The Suppressor grid was patented.
Other tube manufacturers needed a way around the patent of the 5 element Pentode that had a Suppressor Grid.
Aha . . . they came up with a set of beam formers . . . and the Beam Power tube was born. No need for a suppressor grid.
Pretty soon, patents ran out, names were no longer used in the historical way.
Marketing took over with "what would you like us to call it", and the confusion began.
Beam Power Tetrode, and Kinkless Tetrode . . .
Those are actually Beam Power tubes (they have beam formers); marketing just re-named them.
$0.03
Adjusted for inflation