[AMPS] Cathode Driven Tetrodes (more normally...)

[Rich Measures]

>
>OK, I've put Supercathode drive on hiatus, figuring I should start with
>plain old triode-connected cathode-driven tetrodes.  
>There's plenty of published data on 4-1000A in triode-connection, so I
>pulled out my curves and started figuring.
>Once again, my understanding of the instantaneous voltages/currents are
>thus (Please correct me if I'm wrong!):
>0. Grid and Screen grounded.
>1. Drive cathode
>2. "Grid Voltage" on constant-current curves equals (-1)*cathode voltage
>(i.e., when cathode is positive, since grid is grounded, Eg-k is actually
>negative).

When the cathode is driven postive, the anode current cuts off.

>2a. Exact same argument for the screen.
>3. To make it easy, assume a value for minimum instantaneous Eb.  To find
>instantaneous Eb at any particular angle, just DCEb-PeakSwing*sin(angle).
>4. Using the "Three-Halves" power law...the quoted screen voltage on my
>curves is 500V.  So if Eg-k 
>is 300V (peak), at the peak of the driving waveform 

doubtful.  

>	a.  I scale all voltages by 0.6 (300/500)
>	b.  I scale the currents found at the scaled voltage coordinates by
>(0.6)^1.5 (roughly 0.5)
>All other portions of the driving waveform would scale smaller, since Eg-k
>only gets smaller.
>5. Figure out all the conditions using Chaffee formulations.
>
>Well, here's the rub and I am just too dense to get it:

life is to short to get chafed over the Chaffee formulae.  

>I know that the 4-1000A can do GG Triode-connected at 3000V/700mA plate.
>So if Ib,dc is 700mA then the peak instantaneous ib should be around 2.1A.

agreed

>
>But that 2.1A would be the scaled value of ib (since screen voltage isn't
>500V, right?).  So on the published curves, 2.1/(0.6)^1.5=4.2A.  That's
>like ridiculously off-scale on the published curves.
>
>Any more cathode drive than 300V peak and the scaled values all go
>off-scale too.  Besides, it seems to me that 300V peak drive in GG is
>unrealistically high anyway.
>
yes

As I see it, the critical point is when the emission peaks at c. 2.1a.  
and the instantaneious anode potential is minimum.  If a match can be 
made at this point by the tank circuit, the rest of the waveform will 
naturally follow.  

-  later, Scott


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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