Cathode filament power supply

This is a video of an isolation transformer, variac and stepdown transformer working in unison to supply a 0-6 vac supply at 60Hz. Next step is to rectify the output to DC so that it can be used to heat up the tungsten filament.


Here are the videos of the rectification process. First, four rectifier diodes are soldered to the AC output to force all of the negative voltage to be positive. Diodes allow current to flow in one direction. By placing multiple diodes in a certain way, it is possible to direct the current in such a way that the voltage between two leads to remains positive throughout the entire wave cycle.

Next, a resistor (10k) is placed between the DC output wires. This is done to remove any and all floating voltage between the two leads. It is, in a sense, a pull down resistor.

Finally, a large capacitor (1000 microfarad) is placed between the dc output leads to smooth the half wave into a linear output. The capacitor is charged continuously to the peak voltage, and since it is a relatively large capacitor, it only discharges once in a while. If we chose a lower capacitor (0.1 microfarads) We would see more ripples in our DC output because the capacitor would discharge more often.