In the circuit below, the bottom capacitor equals .1 µF and the top capacitor equals .047µF. If the values seem reversed, remember that the reactance of a capacitor is inversely related to its capacitance. The higher the capacitance, the lower the reactance. Of course, the exact values required will probably

differ, but these will be close. Some fiddling is always needed when canceling noise.
    What if the first stage had used a pentode or a cascode amplifier and the voltage division equal virtually zero, i.e. all the power supply noise is present at the plate? In this case, we dispense with the bottom capacitor altogether.

    Tube CAD does the hard math for you. This program covers 13 types of tube circuits, each one divided into four variations: 52 circuits in all. Tube CAD calculates the noteworthy results, such as gain, phase, output impedance, low frequency cutoff, PSRR, bias voltage, plate and load resistor heat dissipations. Which tube gives the most gain? Tube CAD's scenario comparison feature shows which tube wins.

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