[Amps] power limiting in 8410 amps?

[Steve Bookout]

Hi Russ,

I'm not really concerned about the extra 200-300 watts.  I've been using 
them like this for years and all has been fine.

I was just wondering, if they are using some power 'fold back' circuitry.

I just wondered why Alpha would think they NEED to be my 'Mommy' and try 
and limit the output.  It may very well be because without the limiting 
circuitry, some would run the heck out of the amp, far above legal 
limit, and don't think the FCC would care for that.  Also, so many 
'appliance ops' would run them wide open because they could, with no 
regard to long term reliability. After all, the power supply is only 
good for a certain amount of input power.  Would not look good for Alpha 
to have the reputation that they amps will often break down.  (Of 
course, no one reveals that they were driving it with 100 watts, trying 
to get 2500 watts output on RTTY)

I have built many amps over the years, with none of them being too 
fancy.   They were just solid amps.   I've one amp that uses an 8877 
that I built in 1984, that is still putting out an easy 1500 watts.  I 
think the drive power is about 22 watts.  This is in a contest 
environment. I'm not special; so many people can build equally fine amps.

If I can limit my output to legal limits with home brew, non-restricted 
amps, why do I need the 'fold back' of commercial amps?

On 11/2/2018 2:35 PM, Russ Williams wrote:
> Steve.  I would thrilled to get 1200 watts out of my L4B with 40 watts 
> drive Emoji.  I actually know nothing about your amp, but I like to 
> run mine at a fast idle rather than full bore.  If that extra 200-300 
> watts will make the difference in your contesting, then that is what 
> you should strive for.
> About 10 years ago, I converted an AM-6155 control tower amp to 144Mhz 
> and achieved a true 600 watts out using a GS-36B tube and modded power 
> supply.  It ran great---for a while..Emoji
>
> It's all good radio.
>
> Russ KW6T
>
> On Friday, November 2, 2018, 10:41:49 AM PDT, Steve Bookout 
> <steve at nr4m.com> wrote:
>
>
> Hello all,
>
> Over the last week, or so, I seem to remember 'glossing over' messages
> and seeing some comment, by someone, mentioning that 8410 Alpha amps
> have some circuitry that tends to limit their output. This being, done,
> I guess, to get FCC approval.
>
> I ask because, I have 4 of these amps in my M/M contest station and I've
> always noticed that the higher the power out, the more input it takes to
> get there.   They tune up real nice and easy to about 1200 to 1300
> watts, with about 40 watts of drive, but to get to 1500 seemed to be a
> challenge.  Seemed like the gain would fall off, maybe taking twice as
> much power to get the last 200 watts.
>
> Can anyone shed some light on this?
>
> Details would be great, as I would like to maybe remove such limiting
> circuitry.  It just seems like I'm pushing the amp in a bad way to get
> the 1500 watts out.  I know there is no real difference in the effect of
> the power out, but I would rather get 1500 watts out @ 45 watts of
> drive, than 65-70 watts of drive.
>
> 73 de Steve, NR4M
>
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