Hi to the group !
I have a few QRPLabs radios not yet assembled and I'm now considering my power supply options.? I have some hearing loss and tinnitus so a quiet radio/power supply will be a great help.? I have Pyramid brand linear power supplies in both 12V and 13.8V, cheap 12V and 13.8V switchers bought from Amazon and all components necessary to build my own linear supply.? My idea is to feed the chosen power supply through an isolation transformer (Amazon) and to add chokes to the DC output.? I have several of the toroid power chokes sold in assortments by Radio Shack (Radio Shack P/N 273-0108).? There are small chokes in the assortment rated 6 Amp and larger ones rated 20 Amp.??
My questions are, should I go with a linear PS, a switching PS, or build my own linear supply? Will the isolation transformer reduce noise? Can I use several of the Radio Shack chokes in series at the output?? Should I add additional capacitance at the output?? Will a metallic enclosure for the whole project help?? I would also use a standard (Amazon) input line filter before the isolation transformer.? I think this might be overkill but it would be a fun and interesting project.
There are a lot of very technically competent people in this group and I will very much appreciate hearing from you.
Thanks to All and Good DX !
Jim WB4ILP?

There are some good quiet switchers out there, but there are a lot of noisy ones as well.? You'll never go wrong with a linear supply.? They are inherently quiet.? You won't need to mess with any kind of isolation or noise choking with a linear supply.? But linear supplies are bigger and heavier than switchers.? If that's not a concern, go with a linear supply.? Whatever you wind up using, make sure it is regulated and that the output voltage is within the radio's input voltage limits (refer to your radio manual for the specs).?

Here's a tip from and for the frugal ham.? For powering QRP rigs, I've often used old CB-type regulated supplies.? You can buy them cheap at swap meets and garage sales.? On more than one occasion, I've also salvaged the complete regulated power supply sections out of junked solid-state base station CB radios and packaged them up in suitable chassis boxes with a fuse, suitable output connections, an LED pilot lamp, and a 3-wire power cord.? In fact, I have one sitting over on the other side of the shack right now which I salvaged from a junked Royce base station.? Cost me basically nothing and was a fun project.? Most CB power supplies are good for at least 2 amps, which is more than enough to run a typical QRP rig.?
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73/72,
Dean K5DH

Thanks Dean !
OK, it sounds like a linear supply is the way to go.? I have the parts to build one with the possible exception of high capacitance filter caps.? ?How large should the filter caps be for optimum performance?
Jim

For those who are wondering? , this is the type of supply that? JB is considering -

?

It's a fairly basic design by Weber and the PCB is available from Far circuits in Chicago for not much money. However? Mr Weber does
not document his filter calculations at all for this design.

TEF

I have been using a repurposed server power supply for my shack.? ?They are very cheap on Ebay. I bought three of them. think I paid $20 each.? They provide up to 55 amps of power.? ?They're designed to be quiet and run 24/7/365.? They put out 12v but depending on the model can be modified to put out 13.8v.? I modified mine for 13.8v. Works great.?

For my QRP setup in just fine with a battery.?

73
Eric?

I advise against the little buck/boost converters currently available from Amazon and other places.? I wasted many days chasing intermittent problems on a U3S that all instantly went away when I swapped it out for an LM7805.? A large electrolytic on the switcher didn't seem to help either.??

开云体育

Hi Jerry,
I understand your concern with these Amazon units. What problems were you having with the buck boost converter?
I picked one up to throttle my qcx+down to 1 watt for wspr and for other breadboard experiments. Have not noticed any issues. I just want to be aware of what might happen and to keep an eye out for it.

--
regards,
Bryan, N0LUF

Has anyone repurposed an old? ATX power supply from a desktop for the Qrp-Labs gear??

I have one but while well regulated it does not seem very clean compared to other various supplies around the shack.
--
regards,
Bryan, N0LUF

Hi Eric,
Can you provide ordering info for the Amazon unit you bought.? Sounds like a real value at $20 bucks !
Thank You !
Jim WB4ILP?

Unless I missed a posting of his, Eric stated he got these off eBay rather than Amazon.
This means there's a very good chance these are sold out.

Just search for "Server Power Supply".... and scroll. There are quite a few.?

If you find this particular model,? I have pictures and instructions on how to modify it to increase the voltage to 13.8v.

Here's a link to a listing for $18

Thanks Eric,
I found the same/similar items on Amazon.? Yes, I would appreciate the info on the conversion.? I'm sure others here might be interested also.
I guess more than the basic supply I was more interested in everyone's opinion about taking a good linear or switching supply (I already have several) and adding components such as an isolation transformer between the AC mains and the supply's input.? Would this reduce power line noise that might get through to the supplies output? I have read that it would add isolation to power line noise.? Bifilar chokes/caps on the AC input? Adding toroidal chokes on the DC output?? (I have a bunch of Radio Shack # 273-0108).? Additional filter caps at the output?? A full metal enclosures?? Since I have everything in my junk box/parts bins (except the isolation transformer) there is not a lot of out of pocket expense but will it accomplish anything???
I live in a semi urban environment with moderate noise from neighbor's lighting/electronics, a small woodworking company with the usual power equipment and a high voltage power line only 75 yards from where my new wire antennas have to go.
Any input is appreciated.? Jim

If anyone is interested in the mod's for the above server supply, please PM me and I'll get the pictures to you.?
73
Eric

I have one of these kits, the Wall Wart Tamer from Pacific Antenna, but have not assembled it yet. I intend to use it for powering my 12V QMX from my travel trailer power supply.

See:?

Roy - KI0ER?
Littleton, Colorado USA?