Hello Ken,
One reason for few answers to your question might be that, like a lot of
things, it depends. There is not "one true answer". Efficiency is a moving
target with linear AM. Speech pattern is a huge variable.
But, for the fun of it, lets try to get close.
Requirements: Class A, 1500 Peak, 375 Carrier. Ok, here are two figures we
can work with.
Class A efficiency = Lets say 25%, an estimate.
1500 watt output.
1500 / .25 = 6000 watts input required.
6000 watts input - 1500 watts = 4500 watts dissipation at modulation peak.
Efficiency is worse for the unmodulated carrier and assuming traditional
symmetrical modulation, the carrier must be half as efficient as peak
modulation, so...
Class A CARRIER efficiency = 12.5%.
375 watt output.
375 / .125 = 3000 watts input required.
3000 watts input - 375 watts rf out = 2625 watts dissipation at carrier.
The percentage of time you are closer to carrier compared to 100% modulation
determines the average dissipation which will always be changing with
speech.
In this example, the dissipation varies between 2625 and 4500 watts.
I bet a 3cx3000 amp would do it, but it would be a lot happier class B. :)
73',
Jeff/KA5MIR
On Tuesday 14 November 2006 13:59, kenw2dtc wrote:
> Interesting observation. Last week I posed this question on this
> reflector: "If one were to build a class "A" RF tube amplifier capable of
> producing an AM signal of 375 watts carrier and 1500 watts PEP, what would
> be the plate dissipation required by the tube? (I know how stupid and
> inefficient this is, but I really would like an answer)"
>
> In my mind the question needed just a simple answer of plate dissipation
> such as 3000 or 4000 or 5000 watts etc. Instead, I was taken off subject
> to plate modulating an AL-1200, 4-1000 modulators, Viking Rangers, the use
> of the FT-101EE etc.
>
> Of the 18 responders only two guys answered the question: The first guy
> said 700-800 watts and the second guy said 3000 watts. I'm not going to
> submit the same question to the Yahoo Amp Reflector, but based on the 18
> responses, I'm not sure about submitting future questions to this one
> either.
>
> 73,
>
> Ken W2DTC
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