harbach-electronics sk-220 User Manual

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(1) SK-220 “S oft K ey” 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
am plifier.  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.  Rem ove the  perforated top shield.  Rotate the am plifier onto
its side w ith the transform er dow n (it is more s table this w ay).  You are now  ready to proc eed  wit h
the installation.

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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.  Loc ate 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.

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Screw the threaded nylon spacer from the SK-220 kit onto the screw (free d in the previous
step) and tighten well withou t stripping the threads in th e spacer.

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Mount the SK-220  circuit bo ard o nto the nylon s pac er us ing th e 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.

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Unsolder (or cut very near the solder connection) the BLUE wire that goes to the center pin
of the antenna re lay jack on the back pan el.

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Strip about ¼” of insulation from this wire.  Pass the w ire under the nearb y wire harness,
bringing it over near the SK-220 circuit board.

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W rap and solder this BLUE wire to the terminal post on the SK-220 circuit board.

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Pass the BLACK wire from  the SK -220 circuit board under the  wire  harn ess and s older it to
the grou nd lug on the ALC jac k on the re ar pa nel.

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Pass the DARK BLUE  wire from the SK-220 circuit board under the wire harness and
solder it to the ce nter pin of the antenna relay jack on the rear panel. 

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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
20

µ

F capac itor, a 22K  resistor, a diode lead and a red wire going to the antenna relay.

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Dress all wires close to the chassis.