[ARC5] R-508/ARC Conversion

[Rich Post]

My article on the Navy RBS-2 (in The Spectrum Monitor, August 2022),
includes the following note on the power supply.  I used 47 uF caps at 400
volts because I had plenty of those.

"On final testing of the supply with the receiver as the load for both
filaments and B+, the filament side with its 2 ohms added resistance
provided almost exactly 12 VAC. The 1500 ohm total resistance on the B+
side, provided a DC voltage at 216, also nearly on the nose. The alternate
B+ connection ahead of the third 500 ohm resistor was 244 VDC, thus a
calculated B+ draw of about 56 mA. The line power drawn by the supply was
57 watts and 0.52 A according to my Kill-a-watt meter.

Given the size of the UPS transformers, I saw no reason why the supply
would not be able to supply nearly twice the power requirements for this
receiver. If a future project needed 6 volts for filaments, a similar
arrangement using the center tap on the first transformer would meet the
need. The supply could be also stiffened a bit by using larger
electrolytics if needed but there was no detectable hum on the RBS-2 with
the size of the electrolytics I had chosen."

Rich KB8TAD



On Sat, Apr 29, 2023 at 5:20 PM <hwhall at compuserve.com> wrote:

> The older ARRL Handbooks had a graphical solution for selecting the
> resistors & capacitors for voltage doublers.
>
> Wayne
> WB4OGM
>
> -----Original Message-----
> From: Rich Post <kb8tad at gmail.com>
> To: n2lxm at juno.com
> Cc: arc5 at mailman.qth.net; milsurplus at mailman.qth.net
> Sent: Sat, Apr 29, 2023 2:37 pm
> Subject: Re: [ARC5] R-508/ARC Conversion
>
> I needed a power supply for a Navy RBS and decided to build one using
> modern surplus junk, a pair of back to back transformers from dead UPS
> (putting the second transformer from an APS 350 into the empty battery
> compartment of the first UPS, an APS 280.)  I had earlier made a similar
> conversion for powering an ARC 5 transmitter at QRP levels but wanted more
> voltage.  For the higher voltage, I used a doubler on the output.  It
> worked great for the RBS.  Change resistors as needed to get the current at
> the voltage wanted.  Here's pics of the circuit board and the simple
> schematic.
>
> Rich KB8TAD
> [image: The power supply doubler board.JPG]
> [image: 'Impoverished Experimenter' Doubler power supply schematic.jpg]
>
>
> On Sat, Apr 29, 2023 at 12:11 PM <n2lxm at juno.com> wrote:
>
> Greetings All,
>
>
>         Has anyone converted an R-508/ARC using the article in the June
> 1965 issue of 73 Magazine ?. I would like to get this old girl running so
> I can listen in on out local airport Automated weather transmissions.
>
>
>                                                     Jeff N2LXM
>                                           Amateur Radio Operator
>                                                       American
>                                                         Patriot
>                                      Proud Father of Two US Marines
>
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