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Re: [CQ-Contest] ICOM-amp. keying

To: Dick Frey <k4xu@arrl.net>,"cq contest" <CQ-Contest@CONTESTING.COM>
Subject: Re: [CQ-Contest] ICOM-amp. keying
From: David Pruett <k8cc@comcast.net>
Date: Fri, 17 Jun 2005 00:35:03 -0400
List-post: <mailto:cq-contest@contesting.com>
At 11:44 PM 6/14/2005, Dick Frey wrote:
>The Icom's relay is rated at 60V and 0.5A.
>Using this to switch the Alpha's T/R line is about the same as no load.
>The current is < 2mA on key down. That's mouse nuts!
>Go for it, Clive.

I'd be very careful if I were you.

The relay in my IC-756 (non-Pro) is rated (according to the manual) at 16V 
@ 0.5A.  My Henry 2K (modified with a Kilovac HC-1 and a P&B KHU-style 
relay for the input and bias) welded the radio's contacts shut on the first 

My IC-746Pro did the same thing with the VHF-style T/R relays on my 144 MHz 
8877 amp...fortunately, it later un-stuck and has worked fine since.

The relay in the IC-756 is a DIP model with contacts rated as 
described.  However, they seem to be intolerant to inductive kick (yes 
there was a flyback diode across the relay coils).

All homebrew amps at K8CC now have PNP pass devices switching the T/R 
relays.  The radio only have to switch ~ 10mA of base current.

It's easy to build a little box to plug into the ACC2 jack on the back of 
the ICOMs.  I used this for several years until I figured out how to fix 
the '756. 

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