[Amps] Centurion cooling improvement ideas for AM service

[Bill Fuqua]

Sometimes that seems to be the case.
Figure a transmitter using a 1000 watt Plate input triode class C push-pull 
amplifier. At 75% efficiency you would have 750 watts output power. But 
remember your class AB audio amplifier is really running about 60% to 65% 
efficiency so the same tubes would produce 650 or so watts output which is 
not much more than what you really need 500 watts. Also, if it is capable 
of 600 watts the modulator would produce less distortion at the needed 500 
watts. And besides if you have a pair of  810s in the RF amplifier why not 
use 810s in the modulator. That way you would only have to stock 1 power 
tube type and not 2.

73
Bill wa4lav



At 04:27 PM 8/27/2004 +0000, Rob Atkinson, K5UJ wrote:
>Okay Bill thanks.  It seems like I have always seen broadcast tube AM 
>transmitters with modulator tubes that are the equivalent of the rf 
>lineup, i.e. 1 kw out from pair of 3-500s and pair of 3-500s in modulator 
>to provide audio pwr equal to rf carrier and so I thought the audio power 
>had to match the carrier limit for 100% high level plate modulation.
>
>73,
>
>Rob/K5UJ
>
>
>From: Bill Fuqua <wlfuqu00 at uky.edu>
>To: "Rob Atkinson, K5UJ" <k5uj at hotmail.com>
>Subject: Re: [Amps] Centurion cooling improvement ideas for AM service
>Date: Fri, 27 Aug 2004 11:24:56 -0400
>
>At 02:43 PM 8/27/2004 +0000, you wrote:
>>When he says "the carrier is at half level the output is one-fourth the 
>>modulation peak output", he really should be saying that the carrier 
>>VOLTAGE output is at half level and that the power output is one-fourth 
>>peak envelope power out with modulation.
>
>
>>"the carrier is at half level ( as seen on an oscilloscope), the (carrier 
>>power) output is one-fourth the modulation peak output (PEP output)",
>
>
>You should see a positive deflection in plate current of a linear 
>amplifier when modulating. This is not the case when using a plate 
>modulator. That is because the extra power that is going into the 
>sidebands is coming from the modulator. That is why the modulator is 
>chosen to have an output power of 1/2 the plate input power of the class C 
>amplifier.  The amplifier's power supply may provide 1KW which would 
>translate to about 750 watts of carrier output (assuming 75 percent 
>efficiency). And the modulator would add 500 watts to that to provide a 
>total of 375 watts of sideband power on the output or  187.5 watts per 
>sideband (6db down from the carrier). However, the Peak Envelop Power 
>output of the class C amplifier would be 3KW (4 times the carrier power).
>
>73
>Bill wa4lav
>
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