[Elecraft] Using K3 with AMP

[K4GM-George]

For several years I keyed my Dentron Clipperton L amp from the jack on 
my Pro II. I did not use any buffer and it always worked fine because 
the voltage/current being keyed are w/i limitations of the Pro II.  
Without powering up the AMP I ran a cable from the AMP to the jack on 
the K3 I just received.  I noticed that WITHOUT AC power to the amp when 
I moved the standby switch to operate the K3 PTT was keyed and the rig 
put out normal power.  This is w/o the AMP being ON.  Any thoughts from 
anyone? I do have an AMPKEYER available to use between the units but 
thought I could key the AMP  directly. Why would my STANDY/OPERATE 
switch on the amp operate as a PTT switch?  Do I need to set a parameter 
in the K3?  Of course all equipment share a common ground connection.

73, K4GM George