[Amps] AL1200 on AM - max carrier?

[Carl]

I think I should mention that 375W is for a 100% modulated sine wave. Since 
speech is asymmetric and various compression/clipping methods allow much 
higher positive peaks while clipping the negative ones at around 95% a 
higher resulting in more "talk power" for 1500W PEP.
I dont know of anyone that is that fussy to worry about it anyway on AM..... 
or SSB or CW where the amps are tuned for max anyway no matter what the 
power is.

With rigs that permit a single sideband AM the equation changes.

Carl
KM1H


----- Original Message ----- 
From: "Robert Logan via Amps" <amps at contesting.com>
To: "Kimberly Elmore" <cw_de_n5op at sbcglobal.net>
Cc: <Amps at contesting.com>
Sent: Thursday, October 30, 2014 10:16 AM
Subject: Re: [Amps] AL1200 on AM - max carrier?


> Thought I might mention the legal limit for AM is 375 watts carrier.  Bob. 
> NZ5A
>
> Sent from my iPhone
>
> On Oct 30, 2014, at 9:04 AM, Kimberly Elmore <cw_de_n5op at sbcglobal.net> 
> wrote:
>
> Any amp will be inefficient when used as a linear amplifier for AM because 
> as drive is reduced, efficiency is reduced. They will all generate a lot 
> of heat in this application. However, the AL-1200 should hold up well to 
> the lock-and-talk culture. In AM, PEP is 4X the carrier, Overall, you want 
> the carrier to be at 1/4 of the amp's rated PEP output.
>
> Assuming the driver  generates 100 W output, tune the amp for max or 1500 
> W output (whichever comes first) with the amp in SSB mode. You want SSB 
> mode because you want the best linearity. Whether or not you use SSB or CW 
> makes little difference in the efficiency for your application but makes a 
> big difference in linearity.
>
> Usually, when the driving rig is in AM mode, the carrier is reduced to 1/4 
> of the max PEP SSB output. In such cases, you should see no more than 375 
> W carrier power (375 x 4 = 1500).
>
> If you are trying to drive it with an older plate-modulated tube rig, you 
> ill have to be careful if you reduce the power output because the 
> modulation transformer is designed with a particular output impedance in 
> mind. If you reduce the drive to the PA, the impedance changes and you 
> will have to set the proper audio level using a scope or modulation 
> monitor.Start with audio gain at zero, bringing it up slowly. Otherwise, 
> you risk arcing in and destruction of the modulation transformer.
>
> Kim N5OP
>
>
> On Thursday, October 30, 2014 8:05 AM, Gary Smith <Gary at ka1j.com> wrote:
>
>
>
> One thing for sure, run it at the CW
> setting, use the lower KV setting and you
> will run far cooler for a given KW out.
>
> 73,
> Gary
> KA1J
>
>
>> I want to run my AL-1200 on AM for a short stint (2 hours operating
>> time, 50% overall duty cycle). I have tested it at about 225 watts
>> carrier output, and with moderately high duty cycle transmissions (known
>> in the AM crowd as 'Old Buzzarding'), it gets quite hot.
>>
>> What is the max recommended AM carrier power for long-winded 
>> transmissions?
>>
>> Also, I'm assuming it should be tuned up for proper operation at double
>> the carrier power.
>>
>>  I searched the list finding no real answers.
>>
>> Thanks,
>>
>> Tony, K1KP
>
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