Sorry about the keying troubles with your amps, Dave.
Clive's question was about switching his Alpha.
I am very familiar with the control circuit in the Alphas.
Their relay coils are never switched directly from the PTT.
They already have the PNP transistor inside.
In an Alpha amp, you get what you pay for.
The keyed load is 20V at 2 mA - resistive, well within the capabilities
of the quiet and fast but wimpy little relay in the Icom 756.
73, Dick
----- Original Message -----
From: "David Pruett" <k8cc@comcast.net>
To: "Dick Frey" <k4xu@arrl.net>; "cq contest" <CQ-Contest@CONTESTING.COM>
Sent: Thursday, June 16, 2005 9:35 PM
Subject: Re: [CQ-Contest] ICOM-amp. keying
> 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
> PTT-closure.
>
> 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.
>
>
>
>
_______________________________________________
CQ-Contest mailing list
CQ-Contest@contesting.com
http://lists.contesting.com/mailman/listinfo/cq-contest
|