SK-220 "SOFT KEY" INSTALLATION INSTRUCTIONS PART S SUPPLIED WITH T HIS KIT : (1) SK-220 "S oft Key" Circuit Board Assembly (1) 6-32 x ¼" Round Head Screw (1) Nylon Threaded Spacer To start the installation, read these instructions very carefully. Now unplug the amplifier and remove any input, output and control cables that may be connected to the back of the amplifier. Plac e the am plifier on a book, front panel up, and remove the bottom screws holding the feet and case in place. Lift the case up and remove it from the amplifier. Place the amplifier on the bench with the front panel facing you. Remove the perforated top shield. Rotate the am plifier onto its side with the transform er down (it is more stable this way). You are now ready to proc eed wit h the installation. () From the bottom of the chassis, locate the 6-32 nut that is between the tube socket and the rear panel. It secures a screw that holds the RF shield (above the cha ssis ) to the m ain chassis. Locate the screw in the tube com partment that is held in place by this nut (it is near the corner of this compartment at the rear). Loosen this screw and remove the nut and lock washer from the underside of the chassis. Screw the threaded nylon spacer from the SK-220 kit onto the screw (free d in the previous step) and tighten well without stripping the threads in the spacer. Mount the SK-220 circuit board onto the nylon spacer us ing the supplied 6-32 x ¼" screw. Position the board so that it is parallel with the fan cut out edge and the large trans istor is away from the cut out edge. Unsolder (or cut very near the solder connection) the BLUE wire that goes to the center pin of the antenna relay jack on the back panel. Strip about ¼" of insulation from this wire. Pass the w ire under the nearby wire harness, bringing it over near the SK-220 circuit board. W rap and solder this BLUE wire to the terminal post on the SK-220 circuit board. Pass the BLACK wire from the SK-220 circuit board under the wire harness and solder it to the ground lug on the ALC jack on the rear panel. Pass the DARK BLUE wire from the SK-220 circuit board under the wire harness and solder it to the center pin of the antenna relay jack on the rear panel. Pass the RED wire from the SK-220 circuit board under all of the wiring toward the front of the chassis to the terminal strip that holds the +110 VDC supply. Solder this RED wire to the terminal closest to the front panel. Also connected to this terminal are the "+" lead of a 20µF capacitor, a 22K resistor, a diode lead and a red wire going to the antenna relay. Dress all wires close to the chassis. () () () () () () () () () 1 () Replace the perforated cover and top rear plate cover. Reinstall the 15 sheet metal screws holding these pieces in place. DO NOT over tighten these screws, as it is fairly easy to strip the screw threads in the aluminum underneath. Use the book to hold the am plifier while you reinstall the case and feet. () This completes the installation of the SK-220 "Soft Key" module. You m ay not SEE any difference in the operation of your exc iter or amplifier, but you will know that you have reduced the stress on the exciter's keying relay by many orders of magnitude. SK-220 "SOFT KEY" MODULE PARTS LIST R1 & R2 R3 C1 & C2 D1 D2 Q1 Q2 100K ½W 5% 10K ¼W 5% 0.1µF 50VDC CERAMIC 1N4005 (1A 600 PIV) 1N60 GERMANIUM MPS2222 IRF610 HEXFET (N-CHANNEL) HARBACH ELECTRONICS Jeff Weinberg ­ W8CQ 468 County Road 620 Polk, OH 44866-9711 (419) 945-2359 http://www.harbachelectronics.com info@harbachelectronics.com 2 ...