[ARC5] Receiver AC Power Supplies

[Bill Cromwell]

Hi,

It's good to be aware of all of those things. There are going to be 
additional losses for the house supply and at the utility's pole pig 
transformer and over at the local substation things will change a 
little, too - on and on all the way back to the dynamo(es) that generate 
the power. It will even change the demand for a coal mine or a gas well. 
I suspect most of those facilities are up to the task at hand (running a 
command receiver). I stretched the exaggeration to this ridiculous point 
to help emphasize the ham approach (that some people do detest). If the 
iron and other parts that we can often dig out from under tables at 
hamfests are big enough to supply the needed power at appropriate 
(usable) voltages and not burn our fingers then we're good. Engineers 
don't have that luxury when they are designing radios for the millions 
because every fraction of a penny matters. In the case of the 
transformer I am going use for my new B+ I think I'll be closer to the 
limit than I have ever been. Looking at all the ratings of that small 
bit of iron I think I will have some margin of safety but that's a ham 
SWAG factor. When I get it built and operate it into a BC-453 for a 
while then I'll know. I *can* get a bigger transformer. Whether or not 
it will fit inside the box I want to use is another whole question. I 
can also get a bigger box. I hope the bauxite mines will able to supply 
the aluminium smelter and rolling mill for the extra sheet metal <evil 
grin>.

The 25 volt RS transformer will barely get warm after hours of operation 
so none of those losses make much of any real difference running the 
heaters in the command receivers. By the way..all of mine are wired for 
the nominal 24 volt heater supply. I bought one of the 80 meter 
receivers that had been rewired for 12 volts and changed it back to 
original to be compatible with my other receivers. I have now but one is 
real *wreck* by anybody's definition. I got it for some exercise in the 
body shop approach to repair. If it ever resembles a command receiver 
again I'll be sure to brag a lot. Can you spell sledge hammer? Somebody, 
somewhere knows how to use one on command receiver! I'm making some 
progress though.

Somebody asked me about using the regulated DC on the heaters. In the 
aircraft the heaters did run on DC but as far as I know it wasn't 
regulated they way we (I) think of 'regulated'. When the line voltage 
varies the cathode emission varies and in some of the tubes 
(oscillators?) that can make the frequency wobble around. I have 
observed that effect when my shop heater's blower kicks on. There are 
two free running oscillators in those radios. Using regulated voltage 
eliminates that effect - one down, three dozen to go. The extra 
filtering involved will hopefully help keep powerline crud *out* of the 
radio. Two down, two dozen and eleven to go.

73,

Bill


On 12/13/2014 01:27 AM, Fuqua, Bill L wrote:
>    Don't forget, there are I squared losses in the primary as well.
> 73
> Bill wa4lav
>
>