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"Wanna Tinker?" Seriesby Dick Kelly, W6BKY, w6bky@aol.com  When I started this series of articles my assumption was that there is little or no need for a power supply module. My thinking was that power supplies are not very exciting; they are just another tool, like a screw driver or a soldering iron. Not only that, but there are lots of cheap power supplies on the market, as shown in the catalogs from some of the suppliers I listed in article #2. The feedback I have received indicates that I made an invalid assumption. Accordingly, I will, herewith, correct my mistake. If you already have a power supply, please excuse the rest of us while we whomp-up an AC supply for the 40 meter transceiver. In keeping with the philosophy used throughout this series, the power supply module is simple in design, and easy to build. Mine, as usual, was built using mostly salvaged parts. I will, as usual, provide information so you can buy new parts. The circuit shown in Figure 1 will supply approximately 12 volts at up to one Amp. This is adequate to power the 40 meter transceiver we are building in this series of articles.
Figure 1 Want more power (Amps)? No problem! Simply add a "pass transistor", as shown in Figure 2, and get two Amps. Want still more power? That’s easy, too, but we really don’t need it for what we are doing.
Figure 2 T1 has a 25 volt, center-tapped secondary, and must be capable of supplying a couple of Amps. Either a JAMECO #102103 or a Radio shack #273-1512 will serve nicely. Q1 is a 2N3055, or MJE3055. I’ve shown the pin-out for a 2N3055 in Figure 2. The pin-out for the MJE3055 is shown below. Notice that both the MJE3055 and the 1812T regulator come in the TO-220 package ("TO" means transistor outline.)  Unlike the 2N3055 and the MJE3055, both of which MUST be insulated from ground, the 7812T requires both electrical and mechanical contact between it’s mounting flange and "ground". No special mounting hardware is required for the 7812T. Use a small bolt that will fit into the mounting hole and screw it tightly to a metal chassis or heat sink. NOTE: The middle leg on the 7812T is internally connected to the mounting flange. My rule of thumb for a heat sink is: "too much is just about right", and I recommend using hefty ones. Parts layout is not critical for this power supply. Banana jack binding posts make good terminals for the output. JAMECO #125196 or #77690 will do a nice job. F2 in Figure 1 is a one Amp fuse. If you choose to build the two Amp power supply, F2 will, of course, be a two Amp fuse. Use a twist cap fuse holder for F2, and mount it on the front panel for easy access. Use a "slow blow" fuse for F1 and a "fast blow" for F2. Every time you do an "oops", you will blow F2, so keep several on hand.
Figure 3 Figure 3 shows the parts layout I used. I housed my supply in a custom built (home brew) box; 3" high, 5½" wide, and 5½" deep, so you can probably fit yours into a JAMECO #11922, which is about the same size. I don’t show everything in the drawing, but there is enough for you to get the idea. I mounted the 7812T on the aluminum front panel, as shown in Figure 3. The front panel, thus, serves as a heat sink. There must be good metal-to-metal contact between the 7812T mounting flange and it’s heat sink. My front panel, shown in Figure 4, is rather bare with only the output terminals, fuse holder for F2, and an on/off switch.
Figure 4 In addition to parts already discussed, you will need: DIODES D1 and D2 … 1N5400 CAPACITORS (35 volt) C1 … 2200 uF, C2 … 4.7 uF, MISCELANEOUS
(1) 120VAC Power Cord (1) Package, 5-Lug tie point strips, Radio Shack #274-688 Build the power supply, check for correct connections and good solder joints, then plug it in and check for 12VDC at the output. If you do NOT use the pass transistor, the voltage should be about 12 volts. If you are using the pass transistor, the voltage should be about 11.5 volts. If you voltage differs by a volt or more from these figures, you probably have a wiring error or bad solder joint. OK, now that you have a power supply, the next module is the 80 meter receiver "front end", for which you will need the parts listed below. MISCELLANEOUS
1 ¾" x 1 ¾" (1) MV2109 (1) NE602 (1) 78L06 (1) 78L09 (1) 1 mH RF Choke (2) 10.7 MHz IF Transformer (Green core) DC Electronics Part # 41 IF 123 (1) Audio Transformer, RS273-1374 RESISTORS (2) 100 Ohm (1) 470 Ohm
(3) 10 uF (1) 470 uF CAPACITORS, MYLAR OR CERAMIC (3) 0.033 uF (1) 0.01 uF CAPACITORS, SILVERED MICA, NPO, or COG type (2) 1000 pF (1) 470 pF (1) 330 pF
CAPACITORS, ELECTROLYTIC
(3) 0.01 (1) 0.047 ‘Til next time, 73,
Dick, W6BKY
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