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Originally Posted by Apostle Tone
Why? What does this do or what is the advantage of doing this?
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The advantage to doing this is that you don't blow up brand new filter capacitors, or old filter caps that have sat unpowered for a long period of time by "shock charging" them after they haven't had power on them for a long time.
When a filter cap has sat for any length of time or when it is brand new, they appear to the circuit as a dead short to ground, which will cause very high leakage current to ground upon initial power up because the dielectric that seperates the two elements in the capacitor has not been formed/needs to be re-formed. Applying the full power supply voltage across a filter cap with an unformed dielectric/low leakage resistance is fatal to filter caps as the caps will appear as a dead short to ground to the power supply. Upon their first initial charge, by placing that 100K 2 watt resistor in line, you severely limit the leakage current to a safe level so that this cannot happen.
When first powered up with this resistor installed, you will see a high voltage drop when reading voltage across it, indicating that the caps are drawing a high leakage current. As the dielectric forms while you leave power on it, this leakage current will become less and less over time, which is indicated by the gradually reducing voltage drop across the 100K resistor. Once they're formed enough to where they're safe for normal operation, you'll see about 5 volts or less across the 100K resistor, indicating that leakage current is very nill (roughly around 50 microamps) and the dielectric has formed enough to apply the full supply voltage across them.
It's a good idea to do this on brand new caps...on brand new caps that have sat for 5 years or more, it's an absolute necessity. Catch is you have no idea how long the filter caps you've just ordered have been sitting on the shelf unless they have some sort of a manufacture date code on them, which is why you do it everytime with new filter caps.