[ARC5] Receiver AC power supplies.

[DSP3]

Ken,

Truth told, I never considered that excellent  idea.  I don't have any 
hangar queens at this time, but, as mentioned, I'm flush with chokes for 
the moment.   I regularly use the back-to-back transformer trick and it 
works well, to be sure.  I came across some 24v 3A transformers years 
ago and they still do a fine job.  RatShak used to have a nice 12v 3A 
piece but, alas, that item is apparently gone forever...

Jeep - K3HVG


On 12/11/2014 12:16 PM, Kenneth G. Gordon wrote:
> On 11 Dec 2014 at 8:25, DSP3 wrote:
>
>> Now, that's a good project....  I was able to pick up a box full of
>> assorted "iron" at the season's last hamfest.  Included were some
>> smaller filter chokes of the type needed for receiver power supplies.
>> Now, I too can proceed with the power supply project for two 274-N
>> receivers.  Finding reasonably priced chokes is a chore these days and
>> becoming the project critical path item.  But, just in the nick of
>> time........
> If you can find those 3 H 300 VDC chokes, L-15, from hacked-to-ribbons
> command receivers, they make perfectly acceptable chokes for a receiver
> power supply. Trouble is, I suppose, most hackers simply threw them away.
> :-(
>
> My receiver power supplies use back-to-back 110/24 VAC Radio Shack (or
> other) transformers with a voltage doubler rectifier system on the output of
> the second transformer. I use capacitors with as high a capacitance as I can
> buy cheaply (like a pair of 460 mfd jobs), then a small choke, then another
> capacitor on the output. Ripple is VERY low.
>
> You could probably use a series-resistor of the appropriate value in place of
> the choke as was done in many commerical receiver power supplies "back
> then", although I have never yet tried that.
>
> Output voltage of my power supplies is around 230 VDC under load. If you
> want to run your receivers on 150 VDC, take the voltage off the
> center-connection of the voltage-doubler.
>
> I also use the 24 VAC output of the first transformer for the filaments. If you
> get center-tapped transformers, you can then use either 12VAC for
> pre-hacked receivers or 24 VAC for un-hacked or rewired ones.
>
> I was recently given a 110/25.2 VAC at 3 amp transformer by a former
> professor with whom I worked, which came from a defunct furnace control.
>
> It works perfectly for a receiver power supply.
>
> Oh. BTW, I found in an OLD manual that voltage-doubler power supplies
> must have a MINIMUM of 30 mfd capacitance in the filter to prevent too
> much voltage sag under load.
>
> Ken W7EKB
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