[Amps] Actuating a 120 VDC relay with low voltage

[Paul Christensen]

>"OPTO-22 electronic relay.  You can't get much simpler than that." 

If going that route, ensure it's a DC-load solid-state relay -- not the more
common AC SSR type that typically depends on a zero-crossing.  Last time I
checked, the PT-2500A amp has a -110 VDC amp key line.  

Steve, also consider the Keyall device:  http://wb9kzy.com/keyallhv.htm
Easy to build, easy to install, and it doesn't care about load polarity: it
works with positive, negative, and AC amp key lines. 
 
Paul, W9AC