[Elecraft] A question about the KXPA100.

[Don Wilhelm]

Grady,

Is that "250mA at 30 V (max)" the listing in the rig's specifications?
If so, it says that the rig's rating for its KEYOUT (or PTT Out) is the 
maximum it can tolerate without damage.  It normally would be a closure 
to ground (either through a saturated transistor or FET or relay 
points), and source no voltage of its own.

You can easily check that by putting your DMM probe between the PTT Out 
jack and ground.  First set your DMM to read voltage and do a quick 
transmit.  If my guess is right, your DMM will read zero volts when in 
either receive or transmit - proof that the rig does not source voltage 
on its PTT Out jack.  That spec rating is only the maximum voltage and 
current that it can handle from an external device.

If all that is true, then set the DMM to read ohms, and then put it in 
transmit.  The DMM is expected to indicate very nearly zero ohms.

If those things check out as expected you are "good to go".  The KXPA100 
will source 5 volts with a current of 1mA when the KEYIN jack is 
shorted.  That does not exceed either the voltage nor the maximum 
current rating for your rig.

Nothing is needed other than the connecting cable.

73,
Don W3FPR

On 6/14/2017 8:06 PM, Grady Harper via Elecraft wrote:
> I would like to drive the amp with a tx  that shows the PTT Out line to be 250mA at 30 V (max).  Do I need to modify current and voltage from the transmitter to the KXPA100?
> The Key In pin for the amp wants 5V at 1 mA.
>