Archive for March 2011

Winter Project

Mallory _A This is my old Mallory model 12RS6D power supply. It is one of the handiest things I have at my work bench. It provides either 6 volts at 10 amp or 12 volts at 6 amp.  Up to 20 Amp intermittently. What makes it even better is the voltage is variable. Adjustable from nothing to about 15 volts.  Very handy when playing with things.

It is very old. I bought it in the 1980′s, at the auction sale of the contents of an old radio repair shop. This was at the the small neighbouring town of Olivia. I have been unable to come up with a date for manufacture, but I would guess the 1940′s at the latest. If some one could supply me  with more information on this unit, I would be appreciative.

The only complaint I have about the unit is, it is easy to forget the power on. With no light on it, you have to notice which way the toggle switch is sitting. Last week with the snow blowing outside and the wind chill below zero, (that’s about minus 18 degrees Celsius), I decided this would be a good project.


Turning the unit over, the job looked simple.

Digging in my junk (supplies) I came up with a red LED and snap in mounting ring.
I like the simplicity of the design, no bottom cover to get in the way. I can relate to the feeling, if your stupid enough to stick your fingers into the wires, that’s Darwin in action. Note the heat sinks for the rectifiers is the steel case. I like the louvers on the top of the case, had to be designed by a Street Rodder. Common sense, open bottom, louvres on top—no need for a fan.
mallory_Dmallory_EDigging through my stuff I came up with some goodies.

In the days before computers and calculators we used things like this paper slide rule.This one was given away by the Omite Co. of Chicago.
I know that a LED has to have a resistor of the right size in series to keep from burning out. I did my calculations, but being it has been a while since doing anything like this. I did the reasonable thing and got on the Internet. Soon I had all the numbers, that left me feeling good as my calculations were right on. This old man isn’t dead yet.
Luck was with me again as I found a new resister of the right value in my stash of spare parts. See just because something hasn’t been used for 20, 30 or more years doesn’t mean you should discard it.
I wanted to be sure all would work right so I set up a quick test to check it out. All worked as planned, easier to find out you looked at something wrong at this point then after it is all assembled. This is where the various colored jumpers with alligator clips come in very handy.

Sorry about all stuff in the background, I never seem to be able to clear my bench completely.
A gentleman with a better education than me, said as he smiled, that a man’s workbench reflects his mind. I pointed out that being his workbench was seldom used and almost empty, it told a lot about his mind too.

mallory_G mallory_H Here we are drilling the hole for the LED. Notice how heavy the steel in the case is, no skimping here. When this power supply was built, a battery powered electric drill was unbelievable. Electric drills were bulky, heavy, expensive and only starting to become common.
Below you can see the LED from inside the case. The connections were simple solder jobs. The other picture shows the finished job. It doesn’t look much different but the red glowing LED will sure help remind me to shut the switch off.