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KPA1500 on AM

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KPA1500 on AM

Good afternoon,

Does anyone have any tips on running the KPA1500 amp in the AM mode?

73, Lou W2LTF

H 973-726-8300
C 917-270-5421

Sent from my iPhone
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NJ8M

Re: KPA1500 on AM

The max that you can legally run is 375 watts carrier. That on AM will get
you 1500 watts PEP. YMMV. I do not know the spex on the 1500 but that may
put you in the ballpark. Understanding linearity, for AM is covered here:

https://www.w8ji.com/am_linear_amplifiers.htm

If you want to run AM, this is where I would start reading.

73, Morgan NJ8M

BS + MS + $2.98 = COFFEE
Real Life Experience = Priceless, says the man who set his back yard on
fire with a bread board tuner loading a 160 meter inverted L with 1000
watts. LOL

On Thu, Feb 4, 2021 at 1:06 PM Louis Fiore via Elecraft <
[hidden email]> wrote:

> Good afternoon,
>
> Does anyone have any tips on running the KPA1500 amp in the AM mode?
>
> 73, Lou W2LTF
>
> H 973-726-8300
> C 917-270-5421
>
> Sent from my iPhone
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

W3LPL

Re: KPA1500 on AM

Morgan,

The amplifier will actually be outputting its full rated 1500 watts
PEP but because of the 375 watt carrier the heat dissipation
in the amplifier and power supply may be to higher than
they were ever designed or tested for.

If I were you I'd limit the KPA1500 carrier output power to about
200 watts, that should be safe.

73
Frank
W3LPL

----- Original Message -----

From: "Morgan Bailey" <[hidden email]>
To: "Louis Fiore" <[hidden email]>, [hidden email]
Sent: Thursday, February 4, 2021 7:22:13 PM
Subject: Re: [Elecraft] KPA1500 on AM

The max that you can legally run is 375 watts carrier. That on AM will get
you 1500 watts PEP. YMMV. I do not know the spex on the 1500 but that may
put you in the ballpark. Understanding linearity, for AM is covered here:

https://www.w8ji.com/am_linear_amplifiers.htm

If you want to run AM, this is where I would start reading.

73, Morgan NJ8M

BS + MS + $2.98 = COFFEE
Real Life Experience = Priceless, says the man who set his back yard on
fire with a bread board tuner loading a 160 meter inverted L with 1000
watts. LOL

On Thu, Feb 4, 2021 at 1:06 PM Louis Fiore via Elecraft <
[hidden email]> wrote:

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Grant Youngman-2

Re: KPA1500 on AM

In reply to this post by NJ8M

Actually, that assumes that peak to avg is exactly 4. Which it rarely (never?) is with a real human voice.

Aside from the legal (and oft disputed) aspects of AM power limits, you’re better off being conservative and setting drive levels for something under 375W carrier from the amp. Maybe 250-300W. That will ensure you have some headroom for voice peaks (especially if you have a good bit of positive voice asymmetry), keep the amp cooler, etc. And no one on the receiving end will know the difference, anyway. The referenced article is a good place to start.

A monitor scope on the output is essential …

Grant NQ5T

> On Feb 4, 2021, at 2:22 PM, Morgan Bailey <[hidden email]> wrote:
>
> The max that you can legally run is 375 watts carrier. That on AM will get
> you 1500 watts PEP. YMMV. I do not know the spex on the 1500 but that may
> put you in the ballpark. Understanding linearity, for AM is covered here:
>
> https://www.w8ji.com/am_linear_amplifiers.htm
>
> If you want to run AM, this is where I would start reading.
>

Joe Subich, W4TV-4

Re: KPA1500 on AM

On 2021-02-04 3:12 PM, Grant Youngman wrote:
> Actually, that assumes that peak to avg is exactly 4. Which it
> rarely (never?) is with a real human voice.
It also assumes the modulation is symmetrical and that the mic is
wired with the correct polarity.

> A monitor scope on the output is essential …

... and that the deflection on the scope is accurately calibrated
to PEP level (peak voltage across 50 Ohms).

73,

... Joe, W4TV

On 2021-02-04 3:12 PM, Grant Youngman wrote:

> Actually, that assumes that peak to avg is exactly 4. Which it rarely (never?) is with a real human voice.
>
> Aside from the legal (and oft disputed) aspects of AM power limits, you’re better off being conservative and setting drive levels for something under 375W carrier from the amp. Maybe 250-300W. That will ensure you have some headroom for voice peaks (especially if you have a good bit of positive voice asymmetry), keep the amp cooler, etc. And no one on the receiving end will know the difference, anyway. The referenced article is a good place to start.
>
> A monitor scope on the output is essential …
>
> Grant NQ5T
>
>> On Feb 4, 2021, at 2:22 PM, Morgan Bailey <[hidden email]> wrote:
>>
>> The max that you can legally run is 375 watts carrier. That on AM will get
>> you 1500 watts PEP. YMMV. I do not know the spex on the 1500 but that may
>> put you in the ballpark. Understanding linearity, for AM is covered here:
>>
>> https://www.w8ji.com/am_linear_amplifiers.htm
>>
>> If you want to run AM, this is where I would start reading.
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Grant Youngman-2

Re: KPA1500 on AM

Precise calibration of a monitor scope isn’t that terribly essential. An SB-610 or equivalent is hardly a precision instrument, but more than adequate. The point of the scope is primarily to observe and prevent negative peak clipping, ensure you’re not out of headroom and starting to flattop on positive peaks, and adjust mic gain for something approaching 100% modulation.

Grant NQ5T

> On Feb 4, 2021, at 3:26 PM, Joe Subich, W4TV <[hidden email]> wrote:
>
>
> On 2021-02-04 3:12 PM, Grant Youngman wrote:
>> Actually, that assumes that peak to avg is exactly 4. Which it rarely (never?) is with a real human voice.
> It also assumes the modulation is symmetrical and that the mic is
> wired with the correct polarity.
>
> > A monitor scope on the output is essential …
>
> ... and that the deflection on the scope is accurately calibrated
> to PEP level (peak voltage across 50 Ohms).
>
> 73,
>
> ... Joe, W4TV
>
>
> On 2021-02-04 3:12 PM, Grant Youngman wrote:
>> Actually, that assumes that peak to avg is exactly 4. Which it rarely (never?) is with a real human voice.
>> Aside from the legal (and oft disputed) aspects of AM power limits, you’re better off being conservative and setting drive levels for something under 375W carrier from the amp. Maybe 250-300W. That will ensure you have some headroom for voice peaks (especially if you have a good bit of positive voice asymmetry), keep the amp cooler, etc. And no one on the receiving end will know the difference, anyway. The referenced article is a good place to start.
>> A monitor scope on the output is essential …
>> Grant NQ5T