Amps
[Top] [All Lists]

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

To: wlfuqu00@uky.edu, amps@contesting.com
Subject: Re: [Amps] Centurion cooling improvement ideas for AM service
From: "Rob Atkinson, K5UJ" <k5uj@hotmail.com>
Date: Tue, 31 Aug 2004 13:13:55 +0000
List-post: <mailto:amps@contesting.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

_________________________________________________________________
FREE pop-up blocking with the new MSN Toolbar ­ get it now! http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/



_________________________________________________________________
Express yourself instantly with MSN Messenger! Download today - it's FREE! hthttp://messenger.msn.click-url.com/go/onm00200471ave/direct/01/


_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps

<Prev in Thread] Current Thread [Next in Thread>