[Amps] AL1200 on AM - max carrier?

[Roger (K8RI)]

A note on tuning amps for maximum out, or the legal limit on the SSB ot 
CW/tune position?

There are many amps, particularly older ones with a tune and SSB 
position as well as many of today's minimal amps.  By minimal, I mean 
those with a substantial voltage drop under load.

Those older amps were "supposedly" designed to have the same plate 
impedance in either setting. With those, you often would get more power 
out by tuning in the CW/tune position with little voltage sag than 
tuning for max out in the SSB position.

There was the old "tune it where you are going to run it", but many  
didn't realize (or know) that the amps did not have a PS robust enough 
to tune a carrier to max in the SSB position without excessive voltage 
sag which with the higher voltage on peaks would leave the amp 
mistuned.  Many of today's "legal limit" amps suffer from anemic power 
supplies as well as overly optimistic ratings. These amps do not have 
the gusto to operate at their rating in PS and/or tubes. Often the band 
switch and coils are over rated as well, let alone with AM linear.

I'd pulse tune for max and drive it with unmodulated carrier to 1/4 of 
that  (IF the components can handle it), keeping in mind there is a 
legal limit if your amp will go that high.  Remember those old amps were 
rated for and designed for a 1KW input, or 2KW PEP. About half of 
today's legal limit...EXCEPT on AM

In those days, efficiency was considered more important than it is today.

73

Roger (K8RI)



On 10/30/2014 3:00 PM, Glen Zook via Amps wrote:
> The problem is that "desired communications" is not defined!
> If the operator desires to have a 40 dB over S-9 (with S-9 defined as a 50 microvolt signal level) at every location, then that operator can run more power, and still obey the rules, than an operator who just desires that their signal can barely be detected above the noise level. Glen, K9STH
>
> Website: http://k9sth.net
>
>       On Thursday, October 30, 2014 11:00 AM, Drax Felton <draxfelton at gmail.com> wrote:
>     
>
>   And this one too...
>
>
> At all times, transmitter power must be the minimum necessary to carry out the desired communications.
>
>
>> On Oct 30, 2014, at 10:16 AM, Robert Logan via Amps <amps at contesting.com> wrote:
>>
>> 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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