[ARC5] Power Supply Filter Question

[Bill Cromwell]

On 12/20/2013 09:04 PM, Robert Eleazer wrote:
> Back when I first started learning about boatanchors I read the usual ARRL material that described the classic way to build a power supply: a capacitor, an choke inductor, and a capacitor.  I soon found out how rare and expensive the required inductors were.
>
> I was amused last year when I rebuilt the AC power supply on a BC-348-N.  It was classic - literally right out of the Surplus Conversion Manual - using two fairly low valued high voltage caps and a pretty big inductor.  I used some new, bigger, caps when I rebuilt it but left the inductor in place.  Of course, it was also running the B+ way too high and I added some power resistors in both the AC input line and the B+ line.  Got the B+ from over 250VDC down to about 200 VDC.
>
> Now, we have available high voltage caps that have much larger values that those 20 mfd cans we used to use and are a lot smaller as well.  But I wonder if adding some inductance to the power supply circuit would do some good?  Would winding some wire around a piece of steel or even around a nail provide better filtering than just some big caps?
>
> Thanks,
>
> Wayne
>

Hi Wayne,

I'm voting with Bob Macklin for the choke input filter configuration. I 
am going through a Heahkit DX-100 and the "low voltage" plate supply was 
originally configured the same way, capacitor input with a choke. When I 
put in the new cap (where three used to live) I changed it to choke 
input. The low voltage plate supply went from 360 volts to 300 volts and 
everything runs cooler. 300 volts is low? Lower than the 750 volts on 
the final amp plates! That final supply is choke input in the original 
configuration. The new caps are *all* higher in capacitance than the 
originals and smaller too. Way cool!

As per Bruce - I'm looking at using a lot more solid state bits in the 
tube rigs for improved performance and improved reliability. Instead of 
the power supply I'm getting ready to use them in the screen circuits in 
TX driver stages as the drive control. Wire wound power resistors for 
that job are harder to get than they once were.The drive control pot 
(common as dirt) is then used to 'drive' the drive control.

Merry Christmas,

Bill  KU8H