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Re: [Amps] Checking Plate Choke resonance

Subject: Re: [Amps] Checking Plate Choke resonance
From: Larry Benko <>
Date: Tue, 13 Oct 2009 21:45:05 -0600
List-post: <">>

I have no intention of waging a war of words.  Argue as you wish but 
let's build a circuit and analyze it.

I just did a simulation in LTSpice of a tube (voltage controlled current 
source) in parallel with a 2000 ohm resistance which has an open circuit 
voltage of 2828V RMS.  Then I loaded this down with another 2000 ohm 
resistor (for a matched output network) which yielded 1414 V RMS or 
1000W through this resistor.  Then I placed a 100uH inductor (Q>1000) to 
ground simulating the plate choke and at 9MHz calculated a current 
through the inductor of 247mA RMS.  I assume all is well so far.  Next I 
placed a 3.1pF capacitor (Q>1000) in parallel with the inductor which 
resulted in parallel resonance at 9MHz.  Now the calculated currents 
were 247mA RMS through the inductor and 247mA RMS through the 
capacitor.   No change in current at all through the inductor.  Changing 
the circuit to be a series resonant one shows large current in the 
inductor as expected.  If someone can show me a fault in my circuit that 
materially affects the results I will re-simulate it. I can send anyone 
the LTSpice file if they want.

Larry, W0QE

Bill, W6WRT wrote:
> On Tue, 13 Oct 2009 19:37:27 -0600, Larry Benko <> wrote:
>> At a slightly 
>> higher frequency the parallel resonance has a combined extremely high 
>> impedance and very small circulating current.
> Not so. At the exact frequency of resonance, the circulating current reaches 
> its
> peak. 
> One example of this is the working of a grid dip meter. At resonance, the
> circuit under test has the highest circulating current within itself and 
> absorbs
> the most power from the dip meter, thus causing the dip.  
> 73, Bill W6WRT
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