User Guide

2
( ) Solder the RED wire from the SK-401 to the +24VDC lug of the terminal strip near where
you mounted the SK-401. This lug has the positive (+) end of an electrolytic capacitor, the
cathode (banded) end of a diode and a 2.2K resistor soldered to it.
( ) Solder the BLACK wire from the SK-401 to a convenient chassis ground. The terminal
strip described above USUALLY has 1 or 2 ground lugs available for this. One or more
lugs are directly connected to ground as they are used for mounting the large terminal strip.
( ) Replace the bottom cover and any cabling.
This completes the installation of the SK-401 “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 or transistor.
SK-401 “SOFT KEY” MODULE
HARBACH ELECTRONICS
Jeff Weinberg – W8CQ
468 County Road 620
Polk, OH 44866-9711
[phone]
http://www.harbachelectronics.com
[e-mail]
PARTS LIST
R1 & R2 22KΩ ¼ W 5%
R3 10KΩ ¼W 5%
C1 & C2 0.1µF 50VDC CERAMIC
D1 1N4005 (1A 600 PIV)
D2 1N60 GERMANIUM
Q1 MPS2222
Q2 IRF610 HEXFET (N-CHANNEL)