k8bb@comcast.net wrote:
> Oh amplifier gurus ... this is rather long ... I have searched the
> archives, but I don't know what I am looking for ...
>
> I am using an AL-80 and an IC-765 - 50w drive for about 500w out.
> There is an ICE 419 bandpass network between the radio and the amp.
>
> While operating the CQ 160 CW contest (just a little while ago), all
> had been fine for many QSOs. Suddenly, something occurred:
>
> When I hit the F-key to send my call, I heard a "groan" in my
> headphones. I looked up to see the radio and the amplifier - all
> needles all the way to the right - putting out what seemed to be a
> carrier, but waaaaay too much power!
>From what you describe, it sounds like there was oscillation involving the
output stage of the rig, maybe some combination of rig and amplifier. If it
was due to rf feedback, the feedback got in after the point where ALC is
applied in the rig. Any amplifier (in this case the rig's output stages)
will have a combination of frequency and load impedance where it's more
susceptible to feedback and/or oscillation. If it's related to the impedance
the rig is feeding into, then putting an attenuator of 2-3dB in line
directly on the output socket will make a lot of difference.
Steve
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