Re: [Amps] Centurion cooling improvement ideas for AM service

["Rob Atkinson, K5UJ" <k5uj@hotmail.com>]

Thanks Bill, it sure makes sense to me and is probably one of the selling 
points vacuum tube bc xmitter mfrs used.  also, they need some headroom 
because they go to around 120% positive.

Rob/K5UJ

From: Bill Fuqua <wlfuqu00@uky.edu>
To: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>, amps <amps@contesting.com>
Subject: Re: [Amps] Centurion cooling improvement ideas for AM service
Date: Fri, 27 Aug 2004 15:59:09 -0400

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@uky.edu>
> To: "Rob Atkinson, K5UJ" <k5uj@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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