Archer Power Supply Build

OK, so sometimes I search craigslist for:
Oscilloscope
Tektronix
Heathkit

Well this weekend I got lucky, and found someone selling some unbuilt heathkits for a great price.  He also had a few Archer 5V power supply kits for sale, which I’d never seen before, appeared complete, and were reasonably priced.  I bought two, here’s the one that I’m going to build.

In it’s original box:
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Unboxing:

Well, it’s clear how the manual was folded in the box.
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The enclosure and (stick-on) front panel was in flawless shape.
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The circuit board showed some signs of age.  One or two pads lifted a little while soldering, but nothing tragic.
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Components neatly packed within the chassisDSC_0709

Box-O-PartsDSC_0715

The Build

 

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The screw heads were proud of the surface, which would have compromised the front panel application.DSC_0734

And then I remembered I had a drill press and a countersink bit.DSC_0737

The manual suggests soldering the transformer and rectifier together on the bench based on a rough drawing, but given the rigidity of the wire and the tight dimensions, it seemed a better plan was to at least tack-solder the two together while temporarily in situ.DSC_0733

Transformer & rectifier permanently mounted.

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All other elements mounted.DSC_0742

 Testing

Brought it up on the variac with no troubles.  I was able to trim the voltage to 5.46V, and it held across a wide range of line voltages, without a load.DSC_0744

I was unable to calibrate the unit to 5.0V with the stock parts, so first I re-installed the circuit board with the bottom screws in the top holes, so it was easier to access. DSC_0745

Then I soldered in some jumpers in place of R2 and hooked up a decade box. DSC_0749

Then I soldered in some jumpers in place of R2 and hooked up a decade box.  1.8k would have put 5.0v directly in the middle of the trimpot range, but I didn’t have any so I got away with 2k.  I was able calibrate it to 5.0v, and so far it’s been performing without trouble.

You’ll notice that there are actually 4 terminals on this supply.  That’s because this is a ‘sensing power supply’, which allows it to compensate for losses in the wires from the power supply to the load.  The two sense lines can be of a much lower gauge then the supply wires, since they’re not passing any appreciable current.  They sense the voltage at the load, and are part of the regulation feedback circuit.  The regulator’s target is 5v at the load so if it’s gotta output 6.3v to overcome 1.3v of drop, then it happily obliges.

In addition to being fused both at the line side and low voltage side, it also has short circuit protection.

Oh, and here’s the schematic. Doc - Feb 17, 2015, 8-02 PM

I think this is going to be a nice supply for LED tape experimentation.

 

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