Tech Directions- October 2008

5. Per Fig. 2, carefully determine where you will insert the 5-pin socket into the perfboard. Determine the location of each individual pin of the 5-pin socket and mark LED2 the locations with a pencil. Using a #54 drill bit, drill the P-CH ﬁve holes. Insert the 5-pin socket into the perfboard. The 9V 47 Ω N-CH R3 socket should ﬁt snugly. Do not mount the 5-pin socket at Insert any JFET this time. D D 6. Find the locations where you will insert the four S2 R1 100 K mounting screws through the perfboard and attach to the S S G plastic enclosure. Mark each spot with a pencil. Double 9V 100 K 10 μF R2 check the measurements, then drill the holes using a #30 NP P-CH drill bit. S1 7. Attach the push-button switch and the toggle switch PTT to the perfboard. Orient the two switches like the ones shown on the assembly drawing (Fig. 3). Using your ﬁngers, snug the hex nuts down. Per the panel layout drawbright glow is an indication of high transconductance and ing (Fig. 2), insert the 5-pin socket into the perfboard. a dim glow is an indication of low transconductance. This 8. Carefully solder R1 between the center pin of the action occurs as the result of bringing the JFET’s gate to 5-pin socket and the top terminal of the push-button the JFET’s source potential. switch. Refering to Fig. 3, solder two bare jumper wires (about Procedure #24 AWG) to the appropriate I suggest that you ﬁrst build pins of the 5-pin socket. the JFET checker on your proto9. Referring to Fig. 2, insert board so that it resembles the the two LEDs. As viewed from JFET checker shown in Photo 1. the outside of the panel, make This will allow you to see and sure the ﬂat sides of the LEDs physically hook up all neces(cathodes) are opposing, left sary circuit components, as LED ﬂat side down and right LED well as better understand the ﬂat side up. Referring to Fig. 3, JFET checker’s theory of operabend and solder the leads of the tion. right LED to the left LED. Trim All necessary parts are availaway the excess lead lengths. able at Radio Shack and are 10. Referring to Fig. 3, solder listed on the parts list. Refer to Photo 2—Completed checker the schematic diagram (Fig. 1) as you build your circuit. At this stage of the project, you 3.2" will not need a 5-pin socket or the enclosure. 0.25" 0.25" 1. Gather up your parts and start building. 2. After you have successfully built your JFET checker 0.25" 0.25" 0.4" A on the proto-board, tested it, and proven it lab worthy, A D you’re ready to construct the JFET checker that looks 0.1 0.1 c like the unit shown in Photo 2. DO NOT disassemble your 0.1 0.1 2" proto-board circuit. If there is a wiring error in the newly 1.6" built JFET checker, having a unit that works will prove very helpful. B 0.5" B 0.6" 3. Refer to the panel layout drawing (Fig. 2). Carefully A A 0.25" 0.25" measure and mark the perfboard per the indicated dimen0.25" 0.25" sions. Double check your measurements, then carefully cut the perfboard. Place the cut perfboard on top of the A hole: #30 bit B hole: #J bit C hole: #55 bit plastic box. It should ﬁt nicely. If not, ﬁx it. Use mediumD hole: existing grit sandpaper to smooth out any rough edges on the Fig 2—Front panel layout perfboard. 4. Carefully measure and mark the locations to be one side of R3 to the bottom leads of the LEDs. Solder the drilled on the perfboard for the push-button switch and other end of R3 to the [D] pin of the 5-pin socket. the toggle switch as shown in Fig. 2. Double check your 11. Refer to Fig. 3. Using insulated wire (about #22 measurements, then carefully drill the two holes using a AWG), wire the toggle switch terminals TL-BR and TR-BL. #J drill bit. If you do not have a #J drill bit, use a drill bit Solder an insulated wire (about #22 AWG) from MR of the that will allow a 1/4" thread to pass through the hole. Do toggle switch to the top leads of the LEDs. Solder an insunot attach the two switches at this time. Fig. 1—Schematic LED1 N-CH www.techdirections.com ELECTRONICS 25 http://www.techdirections.com

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