Sujet Ampli Fender 5f1 (Champ)

Setting The Screen Voltage
The usual way to set the screen voltage is with a screen dropping resistor from the HT supply. To find its value we need to know the screen current that will flow through it, and then apply Ohm's law.
As a rule of thumb, screen current is a fixed ratio of the anode current. The EF86 data sheet tells us that for an anode current of 3.0mA, screen current is 0.6mA. This is a ratio of:
3.0 / 0.6 = 5.
In other words, the screen current will normally be about one fifth of the anode current, as long as we're operating well away from the knee of the curves. A bias point of -1.5V has been chosen on the load line, as indicated by the green dot. This results in an anode current of about 1.9mA, so we can expect the screen current to be about:
1.9mA / 5 = 0.38mA

Sur la courbe average plate caractéristique de la 6V6 nous voyons courant d'anode a gauche et courant grille écran à droite, avec un rapport de 2.


Alors que quand on calcul par rapport aux données datasheet à Ugs 250v. On a Ia zero signal 45mA, et Igs zero signal 4,5mA. On a donc ici un rapport de 10.