[Elecraft] KX3 To SB1000 Amplifier

[Paul Hvidston]

(had to change email subscription to post to reflector. lets see if this one works...)

The AL80A uses a 12V 100mA relay coil that is pulled to ground to
activate. There is no back-EMF diode in the circuit. The KX3 keying
output is simply the open drain of a 2N7002 low-power MOSFET, also with
no back-EMF protection other than its internal channel diode and an
additional 0.01 uF cap. You could probably "get away" with it, but I
would not recommend it. There is limited protection on the I/O of the
KX3. The lines typically have RC networks to limit RFI and current, but
driving an inductive relay is asking a bit much. A safer solution would
be a simple driver to protect your KX3 from a repair trip to the factory.

On a similar note, the Black Friday sale pushed me off the fence and I
ordered a KX3 (my first Elecraft), woo hoo! I've got an SB-200 that I can hook up
to the KX3 to provide about 80 watts out if I want QRO while saving up
money for a linear for the little guy. My SB-200 has the Harbach keying
circuit so it's good to go. The Harbach circuit was not quite designed
correctly, but that's a story for another list, HI.

vy 72 de Paul/N6MGN, Montana


On 11/29/2016 1:13 PM, David N. via Elecraft wrote:
>  Hello AllI just ordered a New KX3 (Kit)I am wanting to know if Keying My Heathkit SB1000 (Ameritron AL80A)  amplifier with key line off of the ACC2 will be a problemIt says that it is good for 30v @ 100ma. My Amplifier is 12v relay. Not sure current. I would think itwould be fine. But just wanted to check. I won't be able to order my KXPA100 till next year. Have to save the penny's for that one.Thanks
> David KR4OWK2/100 4320
>