[Elecraft] amp keying question

[Dale Boresz]

Hello Dwight,

The External PA Key jack does not source current to drive a relay; 
rather, it sinks current from the relay, so you essentially connect your 
relay between the +12 volt source and the External PA Key jack. So, if 
what you're asking, is how to connect an external relay with a 12 volt 
coil to the External PA Key jack on the KPA100, then...

- If you're using a 12 volt power supply separate from the one powering 
either your K2 or or KPA100, be sure that the external power supply 
ground is also connected to the KPA100 ground.

- Connect one lead of your relay to the (+) lead of your 12 volt supply 
through an in-line fuse holder, containing a 1/2 amp or 1 amp fuse.

- Connect the other lead of your relay to the External PA Key jack 
center pin on the KPA100.

- I'd recommend that you also place a diode such as a 1N4001 across the 
relay coil to suppress inverse EMF when the relay is de-engergized. This 
diode should be connected such that the cathode end of the diode (end 
with the band on it) is connected to the relay coil connection which 
goes to the (+) positive 12 volt line via the fuseholder, and the anode 
end of the diode (end *without* the band)  should be connected to the 
end of the coil which you connected to the KPA100 External PA Key jack. 
(Do NOT reverse the connection of this diode; Q9 in the KPA100 will not 
be appreciative, although your in-line fuse will protect it)

That should do it. When you transmit, your external relay will be 
energized, and you should be able to key your heathkit amplifier via the 
relay contacts.

73, Dale WA8SRA

Dwight wrote:

>So, having tried and not succeeded, does anyone have a circuit suggestion to
>tie in with the External PA Key jack on the kpa100? I need for it to key a
>12 volt relay, so I can use it with my heathkit. Some how, Im missing it....
>  
>