>
>We seem to have lost the thread somewhere along the line.
>
>The original question I posed was to do with the possibility of making an
>output network which ALWAYS provided the correct match to the tube,
>irrespective of power output. As you will see from the various
>calculations, at low power output the RL required is considerably higher
>than at full output.
? However, when the amplifier is driven at low power output, the
required RL is probably not considerably higher because dV/dI remains
roughly the same.
> I realise that the question is a bit academic and
>probably too difficult to achieve in practice. But the concept of
>adjusting the tank network so that it always provides the optimum RL for
>the power level in use fascinates me and I wondered if anyone had attempted
>it.
>
>Why does it fascinate me? Well it has practical applications for an
>amplifier which has to be run from a limited power budget where the
>efficiency is critical.
>
? If I need 100w out instead of 1000w, I switch off my amplifier.
>The average amplifier suffers severe inefficiencies when operated at a
>power output well below its maximum. Also I intuitively believe that the
>linearity must be improved if the anode RL is correctly matched to the
>output network. Anyone come across references to this topic?
>
>John ZS5JF
>----------
>From: Rich Measures <measures@vc.net>
>To: John Fielding <johnf@futurenet.co.za>; Amps Contesting
><amps@contesting.com>
>Subject: Re: Fw: [AMPS] Anode load line calculations.
To: <amps@contesting.com>
>Date: 21 December 1998 08:52
>
>>Both - but what's the difference? An amplifier set up to give 100W using a
>>2000V supply or a 1kW amp using the same ht have the same requirement.
>
>? The requirement is seemingly set by the conditions under which the
>amplifier is tuned up. Assuming 60% effiency, if a 1666w input, w. 2000v
>anode supply, 1000w-out amplifier is, , tuned up at 1666w input, approx
>0.833a of anode current is required. Therefore RL is roughly. 2000v/(2 x
>0.833a) = 1200 ohms and the Pi-network tank circuit must be tuned to
>match 50 ohms to 1200 ohms. Assuming that the drive level is susequently
>reduced until the output is 100w, the anode-V swing is reduced and the
>anode-I swing is also reduced. In my opinion, when the output of this
>amplifier is 100w, RL does not become 22k-ohms. . However, if it were
>decided to tune up the amplifier for operation at 100w out, RL would
>increase to roughly 22k-ohms.
>
>>The point I was trying to make, and which you are conveniently ignoring,
>is
>>that the RL in either case is radically different if you use the formula I
>>posted previously.
>>
>Semi-agreed. . However, the RL formula is an approximation that applies
>for the power level at which an amplifier is tuned. When drive is
>reduced to a tenth, RL does not increase ten-fold. .
>- later, John
>......................................................................
>
>
>
>
>>> From: Rich Measures <measures@vc.net>
>>> To: John Fielding <johnf@futurenet.co.za>; Amps Contesting
>><amps@contesting.com>
>>> Subject: Re: Fw: [AMPS] Anode load line calculations.
To: <amps@contesting.com>
>>> Date: 21 December 1998 03:39
>>>
>>>
>>> >
>>> >But Rich you misunderstand what I am trying to tell you and the
>>others!!!!
>>> >
>>> >The anode voltage swing WILL be the 80% or so of the dc supply voltage
>-
>>> >but it is now developed across a much higher impedance of 22800 ohms.
>>>
>>> ? John: Are we talking about a 100w amplifier using a 2000v anode
>>> supply, delivering 100w - - or are we talking about a 1000w amplifier
>>> using a 2000v anode supply, delivering 100w because of reduced drive?
>>> - thanks
>>> >.......
>>>
>>>
>>> Rich...
>>>
>>> R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>>>
>>>
>>> --
>>> FAQ on WWW: http://www.contesting.com/ampfaq.html
>>> Submissions: amps@contesting.com
>>> Administrative requests: amps-REQUEST@contesting.com
>>> Problems: owner-amps@contesting.com
>>> Search: http://www.contesting.com/km9p/search.htm
>
>
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>----------
>
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
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