[Elecraft] Keying a Hercules from K2

[Jim Brown]

I picked up a used TenTec Hercules amp in very good condition. It works fine from my 
Omni A and Omni V, but I'm thinking that I would also like to drive it with my K2. I've 
looked at the drive from the Omni A, and it appears that 10-15 watts will get me within a 
dB or so of rated power from the Hercules. 

The Hercules was designed to work with the old Omni A, which generates a pre-delay 
keying signal (the call it the "T line") that is +12v on transmit, but transitions roughly 10 
ms before the Omni transmits. (The Omni 5 also generates this signal, but doesn't take 
it outside the radio because later TenTec amps key differently.)  The Hercules keying 
input drives the base of a 2N5087 through 1K, so it isn't going to draw much current.

The doc on the K2/100 says that the 8R line is high on receive and 0v on transmit. An 
app note on the website says that this is a "pre-delay" keying signal that transitions 
roughly 15 ms before the K2 transmits. 

It looks like all I need is a simple inverter (NPN, collector to the amp keying line, emitter 
to chassis, K2 drives the base through 1K) from the 8R line to the Hercules keying line. 
Does this make sense?   

My rig also includes a KPA, but I don't think I need it. It has a key output to drive power 
amps, but there is no doc on it. Is it also a pre-delay signal (that is, 10-20 ms before 
transmit)?  What is its logic -- positive to transmit?  

Jim Brown  K9YC