05-05-2020, 08:49 AM
>If so, there should be AVC voltage at the control grid of the 7A8.
To be picky generally the control grid would be the one closest to the cathode. In pentigrid converter circuits it's use in the oscillator portion. The rf input is actually on grid 4 (pin 6). This where the avc voltage should be found. Grid 1 would have some - voltage on it if the oscillator is preforming properly.
In reality the pentigrid has two inputs. It's like having a triode on the bottom half. Cathode, control grid, and plate (grid 2). And a tetrode or pentode on top. Grid 3 acts as a screen grid speeding up the eletrons. Grid 4 is the 2nd input (control grid for the pentode on top) Grid 5 is the screen for the pentode section. And finally grid 6 is the suppressor grid which is internal connected to the cathode.
Happy Hunting!
To be picky generally the control grid would be the one closest to the cathode. In pentigrid converter circuits it's use in the oscillator portion. The rf input is actually on grid 4 (pin 6). This where the avc voltage should be found. Grid 1 would have some - voltage on it if the oscillator is preforming properly.
In reality the pentigrid has two inputs. It's like having a triode on the bottom half. Cathode, control grid, and plate (grid 2). And a tetrode or pentode on top. Grid 3 acts as a screen grid speeding up the eletrons. Grid 4 is the 2nd input (control grid for the pentode on top) Grid 5 is the screen for the pentode section. And finally grid 6 is the suppressor grid which is internal connected to the cathode.
Happy Hunting!
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
