[R-390] OT: Filter for 9VDC PS

[kenny]

And, for god's sake, do NOT JUST PUT HONKIN HUGE CAPACITORS
> IN THE PS. Yeah, it's real popular among amateur high-end audiophiles,
> which is a good clue you shouldn't do that. The ripple current
> through big capacitors will stress the transformer unduly and
> the huge current spikes 120 times a second is a great way to induce
> buzz into nearby ground loops. Use a reasonable size capacitor
> (giving maybe 10 or 15% ripple on the unregulated supply) and
> take the ripple out with a nice regulator.
>
>   
I had read in an article for a 13.8V @20A power supply that 'a good rule 
of thumb when selecting the filter capacitor is to use about 5000uF per 
Amp'. This article was written by a ham and he also used a regulator 
with  pass transistors.

I have no idea if he is right or wrong but his power supply used 100 000uF!

I have just built a 12V regulated (with an LM317) supply to replace the 
3TF7 in one of my R-390As and I used 2200uF as the filter capacitor and 
I'm already starting to think about stress and long term reliablity on 
the power transformer.