[Elecraft] K3: Keying SB-200

[Don Wilhelm]

Ralph,

If your SB-200 has not been modified, its relay voltage is negative, and 
THAT will cause problems.
The HEXFET in the K3 will take up to 200 volts, but that must be a 
positive voltage.

I would suggest adding a small relay in the SB-200 - rectifying the 
filament voltage at the transformer with a full wave rectifier and a 
capacitor should produce about 8 volts - a resistor could be added in 
series to reduce the voltage at the new relay to about 6 volts.  YMMV, 
but that is the way I would do it.  The original wire to the RELAY jack 
would go to a NO contact on the relay (other side of the contact to 
ground), and the side of the new relay not connected to the newly formed 
power source connects to the RELAY jack.  That way everything is 
contained in the SB-200 and no need for external boxes or sources of 
relay power.

73,
Don W3FPR

Ralph Parker wrote:
> I'm just about to connect the KEY OUT to the SB-200 relay.
> I hope the little transistor in the K3 can take it!
>
> VE7XF
>   
>