fisher X100-3/-A IBAM install ???
- Thread starter ferninando
- Start date
Old thread, but I am installing IBAM and the zener diode mod across the three heaters in my KX-90 (X-100-3). This is all working great, but I am at the lower limit of the adjustability for the output bias. Three tubes I can get right at 32ma, but one is stuck at 35ma at the lowest trimmer setting. The three heaters show around 32VDC across the three zeners.
What adjustment to the resistor values can I make so that I have a little more adjustment range to lower the bias a touch more? The higher bias follows the tube, so I know it is not the IBAM or other circuits, but I would like to tame that one a little more.
I also notice that @dcgillespie says to connect the 5.6K resistor to the cathode bus, but in the schematic drawn earlier in the thread, it is shown connected to ground. I have the 5.6K resistor connected from the trimmers to the cathode bus and not ground, but I am pretty sure that is correct.
What adjustment to the resistor values can I make so that I have a little more adjustment range to lower the bias a touch more? The higher bias follows the tube, so I know it is not the IBAM or other circuits, but I would like to tame that one a little more.
I also notice that @dcgillespie says to connect the 5.6K resistor to the cathode bus, but in the schematic drawn earlier in the thread, it is shown connected to ground. I have the 5.6K resistor connected from the trimmers to the cathode bus and not ground, but I am pretty sure that is correct.