[Boatanchors] Physics of plate current dip

[D C *Mac* Macdonald]

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