[Boatanchors] Physics of plate current dip

[Carl]

With a linear amp it is often hard or near impossible to correlate the Ip 
dip with maximum power out.

It is easier and more accurate to watch grid current in triodes and screen 
current in tetrodes and pentodes. Tune for a peak in those currents by using 
the load control and tune control AND keeping currents within tube specs.

Oft times commercial (and homebrew) amps are not completely neutralized on 
10-15M and plate current dip then does not coincide with maximum power out.

Carl
KM1H


----- Original Message ----- 
From: "D C *Mac* Macdonald" <k2gkk at hotmail.com>
To: <ianmwilson73 at gmail.com>; <boatanchors at mailman.qth.net>
Sent: Wednesday, August 12, 2009 11:11 PM
Subject: Re: [Boatanchors] Physics of plate current dip


>
> Resonance is DEFINED as the frequency of the energy being applied
> to an LC circuit when the Capacitive Reactance (Xc) is exactly equal
> to the Inductive Reactance (Xl).  The "c" and "l" SHOULD be shown
> as subcripts to "X" but I don't know how to do that.
>
> One way or another, the final amp tank circuit is usually in parallel
> with the tube or transistor doing the amplification.  Current existing
> in a parallel circuit is minimum at resonance, but maximum at resonance
> in a series circuit.
>
> 73 - Mac, K2GKK/6
> (Since 30 Nov 53)
> Oklahoma City, OK
>
>
>
>
>> Date: Wed, 12 Aug 2009 16:12:15 -0700
>> From: ianmwilson73 at gmail.com
>> To: boatanchors at mailman.qth.net
>> Subject: [Boatanchors] Physics of plate current dip
>>
>> Tuning a grounded-cathode power amplifier with a pi network goes as 
>> follows:
>> 1. set loading to minimum (maximum capacitance on loading capacitor)
>> 2. tune plate capacitor for resonance as indicated by plate current dip
>> 3. increase loading (reduce loading capacitance)
>> 4. go to 2 until there is no increase in output power
>>
>> I have done a lot of reading on tube output stages and have searched for
>> information online about the mechanism of the plate current dip but with 
>> very
>> little success.
>>
>> Thinking about what happens as the plate circuit is tuned through 
>> resonance,
>> the thing that is special about the resonant condition is that the plate 
>> voltage
>> and current are 180 degrees out of phase only at this point (in other 
>> words, the
>> load presented to the tube is purely resistive at resonance). However, I 
>> can't
>> quite make the connection between this condition and the DC plate 
>> current.
>>
>> Grateful for any enlightenment.
>>
>> 73, ian K3IMW
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