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Re: [Amps] power limiting in 8410 amps?

To: Russ Williams <>,
Subject: Re: [Amps] power limiting in 8410 amps?
From: Steve Bookout <>
Date: Fri, 2 Nov 2018 15:07:17 -0400
List-post: <>
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 <> 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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