[Elecraft] Amplifier Relay Keying Circuit

[Paul Christensen]

Pat,

Are you using the same K3 power supply to provide power to the relay?  Or, 
is it a separate power supply (e.g., a wall-wart type?)

If it's the same supply, then --

1)  The (+) lead from the power supply is tied to one side of the 12VDC 
relay.  If it's a polarized relay (i.e., with internal quenching diode) then 
ensure the supply (+) lead is tied to the relay's (+) terminal; and

2) The opposite relay terminal (-) is then tied to the K3 center Key Out 
jack.  The shield in your diagram is not necessary to complete the circuit.

Upon transmitting, the center KEY OUT jack nearly reaches ground potential 
and the relay closes.  If you're using a separate power supply to the relay, 
you'll need to tie together the negative leads of the K3's power supply with 
the negative lead of the external supply.

In either case, I would consider placement of a suitable fuse in series with 
the relay's (+) lead.

Paul, W9AC