Re: Power supply

Jerry Gaffke
 

The Tekpower TP3005T looks like an excellent bench supply.
A linear power supply using a tapped transformer, so likely cleaner than most switchers,
still reasonably efficient.
Though at $80, kind of spendy for somebody who spent considerably less on their Bitx40.

Here's a cheaper one, this one is a switcher so is probably (but not necessarily if they did it right) noisier:
    https://www.amazon.com/Eventek-KPS305D-Adjustable-Switching-Regulated/dp/B071RNT1CD/ref=sr_1_cc_5?s=aps&ie=UTF8&qid=1543076574&sr=1-5-catcorr&keywords=switching+power+supply+variable+voltage

Lots and lots of cheap switching power supplies that only have one knob to set the output voltage.
Here's a nice 30 Amp switching power supply for use with a 100 Watt transceiver: 
    https://www.dxengineering.com/parts/mfj-4230mv
So for the same price as the Tekpower, you can have 6 times the current out.
You can set the output voltage to anything between 4 and 16 Volts.
The meter can monitor either voltage out, or output current.
Seems to be about as RF quiet as any linear power supply.
But does NOT allow you to set the maximum current like the Tekpower, 
it's always ready and waiting to give your project 30 Amps.

The Tekpower has that extra knob, allows you to set the maximum current.
If you are first checking out a uBitx on receive, you could set the maximum current to perhaps 300ma.
So the Tekpower will deliver 12v to the uBitx (or whatever voltage you set) up to 300ma,
If the uBitx has a short somewhere, the Tekpower then reduces its output voltage until the current is 300ma,
perhaps down to a voltage of nearly zero if that's what it takes.  No burned traces, no smoke.

To check out a zener diode, just put it across the output terminals of the Tekpower and set the max current to 10ma.
(I'm assuming that you can accurately set the current low enough.  May not be the case.)

The way you set the max current is to put a short across the output terminals,
then twiddle the knob for the desired current.

Weird that there are not more supplies that provide this extra knob to set the maximum current,
the additional electronics required is minimal.

There is another form of current limiting that you might want to be aware of:  Foldback current limiting.
If your project exceeds the maximum set current, the power supply shuts down entirely until reset.
Pretty much like a circuit breaker.
This is not as common (or useful) in a bench supply as the simple current limiting of the Tekpower supply.
 
If you want cheap, I suggest going to a second hand store and buy
a 12v desktop "brick" style supply good for 3 to 5 Amps.
If it's too noisy during receive (compare it to running from a 12v battery)
buy another and use the noisy one for other projects.
But these bricks will not have adjustable max output current like the Tekpower.

Jerry, KE7ER

On Sat, Nov 24, 2018 at 07:44 AM, KD8CGH wrote:

Supplies made for amateur radio are usually quiet. You don't need instruments - if you hear the supply in your transceiver it's too noisy.
I have two 30 amp linear supplies, but my precocious desktop space goes to a Samlex SEC123 switching supply. I use a fused distribution box from a Sotabeam kit.
If you are interested in QRP, building kits and different voltages you might consider a bench power supply. I use a Tekpower TP3005T Variable Linear DC Power Supply, 0-30V @ 0-5A which provides current limiting as well as voltage regulation.

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