User Guide

RM-220 RECTIFIER & METERING BOARD INSTALLATION INSTRUCTIONS

PARTS SUPPLIED WITH THIS KIT:

(1) RM-220 Rectifier & Metering Circuit Board Assembly

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. 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.

( ) Remove the 3 large knobs from the front panel.

( ) Remove the nut and washer holding the band switch to the front panel.

( ) Remove the top rear screw holding the right side panel in place along with the 4 sheet

metal screws holding the right side panel.

( ) Remove the 2 Phillips-head screws on the right side of the front panel. This will release the

right side panel for removal.

( ) Remove the 2 Phillips-head screws on the left side of the front panel and loosen the front

panel. 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 circuit board to the tapped

spacers on the capacitor 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. This is mounted behind and to the

left of the 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 marked 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 solder.

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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.
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() 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.
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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.