RM-220 RECTIFIER & METERING BOARD INSTALLATION INSTRUCTIONS PART S SUPPLIED WITH T HIS KIT : (1) RM-220 Rectifier & Metering Circuit Board Assembly To start the installation, read these instructions very carefully. Now unplug the am plifier and remove any input, output and control cables that may be connected to the back of the amplifier. Place the amplifier 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. You are now ready to proceed with the installation. () Remove the 15 sheet metal screws that hold the perforated cover in place and remove this along with the top rear plate cover. Rem ove the 3 large knobs from the front panel. Rem ove the nut and washer holding the band switch to the front panel. Remove the top rear screw holding the right side panel in pla ce alon g w ith the 4 sheet metal screws holding the right side panel. Remove the 2 Phillips-head s crew s on the right side of the front panel. This will release the right side panel for rem oval. 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. Swing the front panel around to the right and support it against the right side of the chassis to prevent undue stress on the wires leading to the panel. Now the old circuit board assembly is fully accessible. Remove the (4) 6-32 x ¼" screws holding the old rectifier c ircuit board to the tapped spacers on the capac itor bank bracket. Swing the circuit board out to gain access to the rear of the board. Unsolder and remove all wires from the board. Cut or unsolder the leads going to the zener bias diode. T his is mounted behind and to the left of th e old rectifier board. The old zener diode is no longer used. It is advisable to remove the old zener diode to eliminate possible HV arcing due to dangling leads and dust. () () () () () () () () () NOTE: All holes noted in the following steps are m arked on the solder side of the new circuit board, and are in a similar location as those on the original rectifier board. () Connect the RED wire coming from the high voltage transformer to hole "D" on the new circuit board and s older. 1 () Connect the HEAVY BLUE wire coming from the high voltage feed-through insulator on the left to hole "J" and s older. Connect the BLUE wire coming from the bottom of the capacitor bank (the + wire) to hole "H" and s older. Connect the BLACK wire coming through the grommeted hole in the chassis (from the relay contact) to hole "E" and s older. Connect the ORANGE wire coming from the meter switch to hole "G" and s older. Connect the YELLOW wire coming from the meter switch to hole "F" and s older. Connect the BLACK wire coming from the plate meter to hole "C" and s older. Connect the RED wire coming from the plate meter to hole "A" and s older. Connect the BLACK wire coming from the top of the capacitor bank (B- w ire) to hole "B" and s older. Connect the bare wire of the 0.001µF 6KV capacitor to hole "K" and s older. Carefu lly inspect all solder joints to be sure that both the joint is good and that there are no solder bridges which could short components together. There are very high voltages on this board. Attach the RM-220 circuit board to the tapped spacers using the previously saved (4) 6-32 x ¼" screws. Place the front panel back in place and loosely put in the 2 Phillips-head screws on the left side of the front panel. Loosely reinstall the nut and washer holding the band switch to the front panel. Place the right side panel in position and hold it in place with the 4 previously removed sheet metal screws. Reinstall the 2 right side Phillips-head screws in the front panel. Tighten all sc rew s in the front panel and the nut securing the band switch. Reinstall the 6-32 s crew, nut and washer on the right rear top of the back panel. 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 3 large knobs on the front panel. correct on these knobs. Be sure that your pointer orientation is () () () () () () () () () () () () () () () () () () Use the book to hold the am plifier while you reinstall the case and feet. This completes the installation of the RM-220 rectifier and metering board. It will provide you with protec tion from diode failure, as well as providing m uch m ore accurate m eter readings. 2 W hen you operate your linear am plifier, you will probably find that the plate voltage reading is much higher than before. This is not re ally the case. The voltage is the same as before, but you are now reading the true voltage. You may notice a slight reduction in the idling plate current of your SB-220. This is becaus e the new board produces 6.8V of bias for the 3-500Z tubes, rather than the 5.1V provided by the original Heathkit design. This will lower the heat produced by the amplifier during voice lulls, but will not materially affect the linearity at high power levels. RM-220 RECTIFIER & METERING BOARD PARTS LIST D1 & D2 D3 ­ D6 D7 R1 R2 R3 R4 R5 5-1N5408 (3A 1000 PIV) 1N5408 (3A 1000 PIV) 8-1N4005 (1A 600 PIV) 1 3W 1% 3600 ¼W 1% 0.82 3W 5% 14-1M ¼W 1% IN SERIES 5600 ¼W 1% HARBACH ELECTRONICS Jeff Weinberg ­ W8CQ 468 County Road 620 Polk, OH 44866-9711 (419) 945-2359 http://www.harbachelectronics.com info@harbachelectronics.com 3 ...