Chuck,
Really, you use the peak voltage (open circuit voltage), and the peak current
(current under load at peak power) with the formula below;
Ra = Va / (1.8 x Ia)
Ra = Plate impedance in ohms
Va = Plate voltage
Ia = Plate current
To me there is some debate about using the 1.8 factor as another ham did some
experimenting and said he found that using 1.87 actually came closer to the
result you want. Below is a link to a GU-43B tetrode amp with all the
calculations that you use. You will see that using 1.87 in fact does work
correctly with a class AB amplifier.
http://www.xs4all.nl/~pa0fri/Lineairs/Frinear1500/FRI1500eng.htm
Best,
Will
*********** REPLY SEPARATOR ***********
On 3/30/06 at 2:34 PM Partain, Chuck wrote:
>So, when I power up my amp, I see 3910vdc on my plate. The way I have it
>configured, I put 330vdc on the screen grid
>and -130volts on the control grid., when I bring the control grid to -69v,
>the tube pulls current. The voltage on the plate is
>dropping to ~3600 to 3700. Is this the value I would use to figure the
>impedance of the tube for tank calculations?
>
> Initial tank settings using ~2k ohm seems to work, but i'm going to rip
>all that out and(try to) make this go from 160 to 15, versus
>what I have now 80, 20 and 40.
>
>forget 10 too much C left.
>
>thanks
>
>
>
>Chuck Partain
>SPG Compatibility Engineering
>maxtor corp
>333 south st
>shrewsbury, ma 01545
>508-770-3496
>
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