Old style power filter ?

[petemoore]

 Circumstances prompt this inquiry: before the 7809 [easily eaten by kanine], power was somehow filtered.
There's a 7809 I ordered around here somewhere, and my last battery is about to become intractably lazy.
My iron feeds a FWR/100uf capacitor and measures 9.1vdc there, powers up my FF just fine but of course has the typical ripple/hum.
Is adding huge capacitence worth the trouble / is there another way to filter the ripple off the DC supply ?
I could surely find a transformer that has around 9VAC at the secondary, and put an LM317 from radio shack on it, but prefer to first explore / exhaust the options at getting this unit going without a regulator [which drops voltage].

[R.G.]

In rectifier setups with a single filter cap, the ripple is inversely proportional to the capacitance. So if the hum is is "typical" with 100uF, then it will be typical -20db with a 1000uF. That man be enough for you to live with until the 7809 arrives or until you calculate the two resistors needed for using the LM317.

Another way to do this is what EH used to do: use a capacitance multiplier. A cap multiplier is (usually) an NPN with emitter to the output voltage pin, resistor and collector to the input voltage from the hummmmm-y power supply to the base, and a cap to ground from the base. The gain of the transistor "multiplies" the capacitance. Actually, it's a crude series regulator. It's not as good as an LM317, and uses a resistor and a cap instead of two resistors compared to the LM317, but - well, this is experimentation, not stage use, right?

[PRR]

Much-much better than a one-C filter is a C-R-C filter. Put in as much R as your voltage-drop can tolerate, big cap on each side of the R.