[Amps] Overdrive protection

[Mike]

Hello Bert,

Thanks for the info. on how to tame the IC746 overshoot.  Too bad I didn't
learn about the 746's overshoot problem or your approach to tame it until
it cost me a 4CX1600 in a HB amp.  Changed to a GS-35B and just let the
first couple of msec. overshoot happen.  Most of the time you can see the
1600 to 1700 W initial output on a peak reading Wattmeter.

  73,
  Mike, K4GMH

On Fri, Jul 27, 2012 at 9:42 PM, Bert Almemo <balmemo at sympatico.ca> wrote:

> There is a simple solution. I use a 9V battery and a pot to set an
> appropriate/fixed ALC voltage to my 746 for the drive power I want. Works
> like a charm and no overshoots.
>
> 73 Bert, VE3NR
>
>
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Joe Subich, W4TV
> Sent: Thursday, July 26, 2012 10:51 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Overdrive protection
>
>
> > I don't see why the ALC can't be adjusted so the amplifier is never
> > over driven
>
> The problem is that the transceiver ALC time constant is too slow and the
> transceiver IF stages have excess gain.  Thus the transceiver makes "full
> power" for the few milliseconds *before* the ALC can react and reduce the
> gain.
>
> It happens in nearly all brands of transceivers - including Yaesu's
> FT-1000D, FT-1000MP, FT-1000MP MKV (I haven't tested an FT-2000 or 5000
> yet)
> and all of the Icom 756 series, 7600, 7700, 7800 *IF* the If gain
> adjustments (factory) are too high.  Since many of the rigs have firmware
> based, per band gain settings, a given radio can have tremendous overshoot
> on one band and be fine on another.
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 7/26/2012 10:27 PM, Ron Youvan wrote:
> >     Mike G8TIC/M0VHF Tubby wrote:
> >
> > /*snip*/
> >> I cannot see the point of (over) driving an amplifier and effectively
> >> using ALC to "hold it back" ... it just seems to me that if you're
> >> doing this then your amplifier isn't big enough in the first place -
> >> to this end I have to say I'm with Mr. Measures... a 3CX3000 or
> >> 3CX5000 under-run at 1500W PEP is just going to be SO SO much nicer
> >> than a small amp thrashed to within inches of its life ;-)
> >
> >     I don't see why the ALC can't be adjusted so the amplifier is
> > never over driven and is kept at the desired operating drive level.
> > I actually thought that was the idea.
> >
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