On Sat, Jan 30, 2010 at 08:12:47PM -0800, Bill, W6WRT wrote:
> ORIGINAL MESSAGE:
>
> On Sat, 30 Jan 2010 22:40:47 -0500, Roger <sub1@rogerhalstead.com>
> wrote:
> >With full carrier and full output, you can also adjust the ALC so it
> >just becomes active. Then when talking keep the drive down to the point
> >where you are just under where the ALC becomes active, but don't use the
> >ALC to limit the output or it'll really splatter.
>
> REPLY:
>
> There are two kinds of ALC and I think Roger is talking about the kind
> of ALC that is fed back from the amplifier to the transceiver. With
> that kind, I fully agree with the above.
>
> But there is also ALC that is generated entirely within the
> transceiver (such as my IC-756Pro3), and is completely independent of
> the amplifier. With that kind you can safely use ALC to limit the
> drive and it does an excellent job, I might add.
>
> And if you use the internal type of ALC, you don't need the fed-back
> kind at all.
I do feed the ALC output of my AL-80B back to the exciter. The 80B
has an ALC sensitivity adjustment on the front panel, so I can somewhat
control the PO of the exciter from the amp. However, it is imperfect
in that either the amp or the exiter is too slow in responding, resulting
in an initial onset (of either carrier or voice) that briefly reaches
full power output before the ALC feedback takes effect.
I can certainly see how that might cause splatter (I think it is
sometimes referred to as "buckshot") if the amp is not properly tuned,
but if the amp is tuned for full power, the signal is clean; the audio
just gets "thinner" as I turn the ALC down towards zero.
However, because it really doesn't control PEP output very well, I don't
use this mechanism. I do leave the ALC connected, though, and adjusted
to come into play at just above the level of power I am using, because
I figure it might protect the tube and/or amp in the event of a
catastrophic failure -- say the antenna becomes disconnected during a
transmission. It's certainly not as fast or failsafe as a built-in grid
overcurrent protection circuit, but I rather suspect it's better than
nothing.
I suppose YMMV,
Rob / KD8WK
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