>
>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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