[Elecraft] K3 interface to Collins 30L1

[W9HAK]

Hello John,

My K3 is driving my 30L1 without any problems.  However I did need to 
construct an interface to key the amp.  The key line is a -170 vdc and 
requires 100 ma. to actuate the relay.  You can check this by measuring 
the - volts before keying.  And then put a ma meter in series to ground 
and measure the keyed current.  No drive required for these measurements.

I used a NPN high voltage transistor,  (NTE 397),   for the interface.  
And a couple of resistors all in a small plastic box. 

The collector is attached directly to the keying line of the 30L1.  I 
attached the emitter of the transistor  the 12 dc supply on the rear 
apron of the K3.  I attached the base of the transistor through a 2.7k 
resistor to the key output on the rear apron of the K3. Between the base 
and emitter I placed a 4.7k resistor.   Noting trick about the 
arrangement but you want to be sure that the transistor is saturated for 
cool operation.

Smith Bradford
W9HAK