Harbach Electronics SK-201 User Manual

SK-201 “SOFT KEY” INSTALLATION INSTRUCTIONS

PARTS S UPPLIED WIT H THIS KIT:

(1) SK-201 “Soft Key” Circuit Board Asse m bly (1) Nylon Threaded Spacer (2) 6-32 x ¼” Screws (1) 2-Lug Term inal Strip (1) #6 Lock Washer

To start the installation, read these instructions very carefully. Unplug the amplifier and remove any input, output and c ontrol cables that may be connected to the back of the amplifier. Remove the chassis from the case and remove the perforated sheet metal RF shield from the top of the chassis. Remove the tubes and put them in a safe place. You are now ready to proceed with the installation.

( ) Turn the amplifier over so that the rear is toward you. Locate a point that is 8” from the

right edge of the chassis and 4½” from the rear of the chassis. Mark this p oint.

( ) Very carefully drill a hole that will clear a 6-32 screw at the point you just marked (#27 drill).

Do not use too much pressure because you want the drill to stop after just penetrating the

chassis. Clean up any burrs from the hole.

( ) Rotate the chassis so that it is on it s side w ith the tra nsform er do wn (it is more s tab le that

way). Push (1) 6-32 screws through the hole from the tube side of the chassis. Put on a

lock washer and attach the nylon spacer onto the screw (on the underside of the chassis

and tighten.

( ) Inside the tube compartment, locate the screw that fastens the RF shield to the chassis and

secures terminal strip “Q” to the underside of the chassis. Terminal strip “Q” is a 5-lug

strip mo unted at a right angle to the re ar of the chassis. Loosen this screw and remove the

nut while keeping the screw through the chassis.

( ) Place the hold down lug of th e supplied 2 -lug terminal strip o ver the end of the 6-32 screw

(the one you just removed the nut from). It may require some adjustment of the wiring

harness to make roo m for the strip. The s trip sho uld be oriente d app roxim ately para llel w ith

the existing terminal strip “Q”.

( ) Reinstall the 6-32 nut onto the screw and tighten . Now turn the amplifier over (botto m up).

( ) Locate the 33Ω 1W resis tor going from the antenna relay jack on the rear panel to a solder

lug at the end of the primary voltage selection strip. Unsolder the res istor from the jack and

move the end so that it goes through the insulated terminal on the 2-lug terminal strip you

just installed. DO NOT solder yet. Leave the 0.02µF disc capacitor connected to the

antenna relay jack.

( ) Install the SK-201 circuit board on the nylon spacer with a 6-32 x ¼” screw. Orient the

circuit board with the long side parallel with the rear of the chassis and the TO-220

transistor away from the rear of the chassis.

( ) Connect the BLACK wire from the SK-201 circuit board to the grounded lug of the 2-lug

term inal strip (installed ea rlier) and solder.

( ) Connect the YELLOW wire from the SK-201 circuit board to the insulated lug of the 2-lug

terminal strip and solder (along with the 33Ω 1W resis tor).

( ) Connect the BLUE wire from the SK-201 circuit board to the antenna relay jack on the rear

panel and solder (along with the 0.02µF capacito r).

( ) On the terminal strip to the left of terminal strip “Q”, locate the junction of the rectifier diode

and the 10KΩ 2W resistor. Connect the RED wire from the SK-201 circuit board to this

junction and so lder.

( ) Fish the GREEN wire from the SK-201 circuit board under the capacitor going between

terminal strip “Q” and the terminal strip to the left, over the wire bundle and through the

gromm et in front of the SWR bridge assembly.

( ) Rotate the chassis onto its side with the transformer down. Pull the GREEN wire all the

way through the grommet so that it reaches one of the terminal lugs where the filament

choke is soldered. Solder the GREEN wire to o ne of the lugs where t he filam ent choke is

attached.

( ) Reinstall the tubes and the perforated sheet m etal RF s hield on t he top o f the chassis and

put the chassis back into the case.

This completes the installation of the SK-201 “Soft Key” module. You may not SEE any difference in the operation of your exciter or amplifier, but you will know that you have reduced the stress on the exciter’s keying relay by many orders of magnitude.

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