[ARC5] Converters for Q5-ers (PS hum)

[Bill Cromwell]

Hi,

I have found that running my BC-453 on pure, battery supplied DC makes a 
tremendous difference. The difference between playing radio or playing 
the accordion (different hobby) instead. The apparent source of 
background noise is man made crap and crud coming in on the power line 
and not so much the 50/100 or 60/120 cycle hum. I fretted and studied 
and poked at the incoming noise and suspected my antennas for a long 
time and frankly considered just giving up radio entirely! My final, 
desperate act was setting up batteries to operate the BC-453. Epiphany 
time! In my case the DC heater line *does* make a big difference but it 
might be defeated if the DC is derived from the AC line without good 
filtering on the AC line at the input. Next I am going to visit the AC 
input filters that are supposed to be installed on *ALL* switching power 
supplies but are often omitted. I tamed a PC by installing the parts 
that had been jumpered/omitted.

I use a pair of 12 volt lead-acid batteries in series for the heater 
strings, and I started with ten 9-volt batteries in series for ~90 volts 
B+. Then I tried it with five 9-volt batteries and I got the same result 
with about half the current! So 45 volts it is. If there was any 
difference in volume in my cans I could not notice it. Running speakers 
from across the gymnasium might be different.

The other difference the DC on the heaters might make is when the DC is 
regulated so the heater current is stable. The two L-C oscillators will 
drift noticeably as the AC line voltage varies with load changes - such 
as when the blower on my furnace comes on. When the blower turns off 
again the oscillators drift back the other way. I don't miss that, either.

If I had spent the amount of time practicing with my accordion that I 
*wasted* trying to clean up the signals with antenna changes I would 
enjoy both hobbies a lot more <wink>.

Just my personal results.

73,

Bill  KU8H

On 01/20/2015 12:06 AM, Kenneth G. Gordon wrote:
> On 20 Jan 2015 at 12:59, Leslie Smith wrote:
>
>
>
>> DC filament supply v AC filament supply. Does AC to the filaments
>> matter?
> No. Not one whit. Absolutely not.
>   
> Ken W7EKB