MM-220 OR PM-220 METER REPLACEMENT INSTRUCTIONS PART S SUPPLIED WITH T HIS KIT : (1) MM-220 or PM-220 Replacement Meter (Multi-Meter or Plate Meter) (2) Panel Drilling Templates To start the installation, read these instructions very carefully. Now unplug the amplifier and remove any input, output and control cables that m ay be connected to the back of the amplifier. Place the amplifier on a book, front panel up, and remove the b ot to m sc re w s 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. You are now ready to proceed with the installation. () Remove the 15 sheet metal screws that hold the perforated cov er in place and remove this along with the top rear plate cover. Rem ove the 3 large and 2 sm all knobs from the front panel. Rem ove the nut and washer holding the band switch to the front panel. Remove the nuts and washers holding the meter switch and sensitivity pot to the front panel. Rem ove the 2 Phillips-head screws on the right side of the front panel. Remove the 2 Phillips-head screws on the left side of the front panel and loosen the front pane l. It may require a slight prying action with a screwdriver to separate the front panel from the chassis due to paint stickage. Pull out the pilot lamp assem blies from each meter. On the back of each m eter remove the nuts that secure the solder lugs to the m eter. Remove the terminal strip attached to the front panel. The lower left nut on the plate current meter fastens it. The front panel should now be free. Remove and save the m ounting nu ts for both meters and remove the meters from the panel. The panel should now be free of all parts except for the Heathkit logo. Take a mom ent to clean the face of the front panel with hot water and dish wa sh ing detergent. Cut the supplied template sheet in half to separate the two templates. One of these is a spare. Place one of the templates on the rear of the front panel and very care fully align the hole patterns of the meter being replaced. The adjacent meter should be very close to also being aligned (holding the panel up to a light source will aid in alignment). Hold the template in place with tape so that it will not move during the following operations. Now check the alignment again. 1 () () () () () () () () () () () () () () () Carefully center punch the new upper right and lower left mounting holes. Drill these holes w ith a 1/16" drill, keeping the drill perpendicular to the panel (a drill press helps, but is not necessary). Drill out the upper right hole with a 1/8" drill. If you have a 3/32" drill bit, use it to enlarge the lower left 1/16" hole, otherwise carefu lly enlarge this hole with the 1/8" dr ill. Th e drill will tend to drift into the larger (old) hole. The final size hole is to be 1/8". A small rat-tail file would be useful in cleaning up this hole. Punch through the tem plate near the upper left notch to be cut in the front panel. W ith a sm all rat-tail file make the indicated notch in the meter cutout hole. A triangular file or the edge of a rectangular file may also be used to make the notch (the notch does not have to be round). Remove the tem plate from the panel and trial fit the new meter. This w ill indicate whether more filing is needed to obtain a good fit and have the top of the meter parallel with the top of the front panel. W hen a good fit is obtained, fasten the meter to the front panel with the supplied washers and nuts. If the plate meter is being replaced, leave off the washer and nut f ro m th e lo w er left stud (view ed from the rear of the front panel). Unsolder the m ete r leads and bypass capacitor from the solder lugs that went to the old meter. Cut the black and white leads going to the lamp assem bly removed from the old meter. Cut these leads close to the lamp assembly and strip about 1/8" of insulation from each end. W e will now reas semble the front panel. Bring the front panel up to the front of the amplifier chassis and put the meter switch and sensitivity potentiometer shafts through their respective mounting holes. Loosely install the mounting washers and nuts. Reinstall the meter leads on the meter not being replaced and tighten the meter terminal nuts. If the plate meter is being replaced, place the supplied flat washer over the remaining mounting stud, then the meter light terminal strip and finally the mounting nut. Tighten the mounting nut firmly. Looking down at the back of the front panel, loop the RED meter wire through the "+" terminal of the new meter (the terminal nearest the right edge of the front panel). DO NOT solder yet. Loop the BLACK meter wire through the "-" terminal of the meter. DO NOT solder yet. Loop the leads of the bypass capacitor through the two m eter terminals and solder two leads on each meter terminal lug. Connect and solder the meter lamp leads to the top solder lugs on the meter. These are the internal lamp connections. 2 () () () () () () () () () () () () () () () () Reinstall the lamp assem bly into the meter not being replaced. Bring the front panel up to the chassis. Put the tuning capacitor, loading capacitor and bandswitch shafts through their respective holes. Hold the front panel in place with the bandswitch m ounting washer and nut (loosely installed). Replace the (4) 6-32 Phillips-head screws at each corner of the front panel. Secure with a lock washer and nut and tighten firmly. Tighten the nuts holding the bandswitch, m eter switch and sensitivity potentiom eter. Place the loading capacitor and tuning capacitor in their fully meshed position. Turn the other 3 shafts to their full counterclockw ise position. Now reinstall the 3 large and 2 sm all knobs. The tuning and loading capacitors each point directly to the left (9 o'clock). The bandswitch knob points at 80. The sensitivity po te nt io m eter points at 7 o'clock and the meter switch knob points to "GRID". 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. Reinstall the case and feet using a book to support the amplifier. () () () () () This completes the replacement of a panel meter on your SB-220. Y ou w ill notice s mall differences in the action of these me ters as the ballistics are different from the original Heathkit meters. They are as accurate, how ever. HARBACH ELECTRONICS Jeff Weinberg ­ W8CQ 468 County Road 620 Polk, OH 44866-9711 (419) 945-2359 http://www.harbachelectronics.com info@harbachelectronics.com 3 ...