[ccomer1955]

I'm pretty happy with my AES radio power supply kit, but I have a few modifications I'd like to look into. I've made a wooden box for the supply with a report battery label on it, and I used brass knurled nuts to make terminals across the top of the box. I haven't mounted the supply in the box yet, but I'd like to place a toggle switch and fuse on the mains line. I would also like to place an LED power on light in the circuit, but I thought I'd seek advice here for the best place the put the power on light that will have the least effect on the power supply.

Any suggestions for the power on light or for that matter any other mods I might want to consider?

[morzh]

What voltages and currents do you have in there?

[ccomer1955]

The transformer is AES part # P292. 


Primary Voltage
120 V
Secondary 1
140 V @ 100 mA
Secondary 2
28 V @ 20 mA
Secondary 3
10.5 V @ 2 A

Here is a scan of the schematic:

[ccomer1955]

I'm pretty close to finished with the box. I just need to make the internal harness, add the toggle switch, and figure out where to place the LED circuit...maybe put a power supply fan in the side.

[morzh]

Secondary 3, LED in series with 2K to 10K resistor depending on the LED efficiency and desired brightness.

[ccomer1955]

The LED works perfectly hooked up as you described. I also have a small fan that I'd like to place on the box directly in front of the A voltage regulator's heat sink. The fan is 12 volts and 0.06 amps. Will a 1 watt 300 ohm resistor work across the second secondary (28v at 20ma) to bring the voltage and amperage down enough for the fan?

[morzh]

not sure how you want it: your secondary is 20mA and yu want to load it more while your fan needs 60mA?

I would try the same output as for LED, it has enough oompf A-wise and a 12V fan might work just fine from 10.5V unless it has undervolt cutout which is rare.

[ccomer1955]

I tried placing the fan across the third primary, and it works, but seems to turn a bit slow. I also think my fan might be too small for my purpose, so I might drop by the computer parts store tomorrow.

[morzh]

yes it will be a bit slow, it is down 13%.

Here's an idea: measure D3 output, see if it is close to 12V.

[ccomer1955]

I measured the D3 output, and it is close to perfect. 12.47 vdc. Will the .47 vdc hurt my fan?

Thanks for the expert help, I now have a wiring harness for inside the box to the voltages I need for the two radios I use with it, a toggle switch and fuse on the mains, a red LED power on light, and a 12vdc fan for the heat sink. Later, I will cut and drill some holes and mount the power supply in the box.

[ccomer1955]

Got the battery box sorted. Toggle switch and fuse, red LED power on light, 12vdc fan, and the voltages that will make the 20s radios I own work. The lug on the side is connected to the common ground, but I don't know if it's a good idea to use it. I've heard both arguments for and against it. I think I will take it apart now and give it a nicer finish and get a fan protector cage, but it works, and it ain't ugly exactly. Maybe my wife will let me put one of the 20s sets in the living room now.

For the record, I placed the LED across the third primary in series with a 10K resistor, and the fan just above C4 at the D3 output (which showed 12.47vdc on my mutilmeter). Please advise me if any of you see an issue with either placement.

[morzh]

No issues. However if you want peace of mind, 8 Ohms resistor in series with fan will drop about what you have above 12V. And it can be a small 1/8 or 1/4W resistor.

[Arran]

 I don't think that the fan will be necessary with the LM317T, they don't run hot enough to cause trouble so long as the heat sink is of sufficient size. There are big stereo amps that handle more current then any of the semiconductors in this power supply, and all they use are large convection cooled heat sinks. I would keep the extra secondary free in case you want to add a "C" supply to the unit.
Regards
Arran

[Raleigh]

Nice looking "battery" box. The brass hardware is a good touch, and the labels look good.

Do you have a vent for air intake (or exhaust, depending on the direction of the fan)? The fan won't do much good without a way to let the air flow through.

[ccomer1955]

I have the fan about two and a half inches from the heat sink on the LM317 blowing directly on it. Putting a vent on the other side of the box wouldn't be difficult. Probably the easiest way would be to drill some holes in a pattern and stain the insides of the holes. Think I should? The box itself is inverted on its lid, and I have the lid screwed down on all four sides with the box itself about half an inch above the bottom of the lid. While that's not an actual vent, it does provide some avenue for air to be forced out of the box, but I'm sure I can figure out an aesthetically pleasing way to make vent on the other side from the fan.
Eventually, the plan is to watch this one for a while to see if the PS develops any problems, then make one like it for each of my battery radios, so I don't have to take the PS down and put it back together all the time each time I use a different 20s set. I'm sure I can find a better looking box to use than this Michael's craft box. too.