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Old 25th March 2009, 10:41 PM   #1
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Default Dumb Question Brain is numb today!

I know I will get a bunch of posts calling me a flake but I need help.

Using a triode curve for a SINGLE section of a dual Triode. I am trying to plot some load lines for the two sections in Parallel. Voltage stays the same, current doubles, but what do I plot for the Load ? Twice the OPT or Half or Same (assuming I double the plate current on the graph)???
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Old 26th March 2009, 03:26 AM   #2
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Plot it with a single plate characteristic using half the current and twice the load resistance.
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Old 26th March 2009, 03:41 AM   #3
nhuwar is offline nhuwar  United States
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Twice the plate load,,, in parallel,,,, wouldn't it be half the plate load?



Or did I miss something?



Nick
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Old 26th March 2009, 03:54 AM   #4
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doesn't twice the load resistance = half the plate load?
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Old 26th March 2009, 04:01 AM   #5
nhuwar is offline nhuwar  United States
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If so I've learned something, which would be a good thing LOL.



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Old 26th March 2009, 04:19 AM   #6
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Well, I've always thought of a large load as a small resistance. I mean its like gear ratios, high gears are lower numerically. Are we talking about a large number or a heavy load for the amplifier stage?
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Old 26th March 2009, 05:02 AM   #7
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It seems that there's some confusion as to what you mean in postulating your paralleled pair of tubes.  If you are looking at a set of plate curves, and have settled on an operating point of x volts and y milliamps, and have figgered the gm, rp and µ for this condition, with the two devices in the envelope operating in parallel (assuming they are identical):

rp will halve

gm will double

µ, and thus circuit gain will thus remain the same

optimum load, though (which is a function of rp) will halve

current drive into the load (if it is a difficult one like an 845, this is a real improvement) will double.

Did I explain that okay?

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Old 26th March 2009, 01:44 PM   #8
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I think I understand,

Using a single plate curve,

Plot with twice the load resistance and then I can double the currents for what will actually flow at any given grid voltage?

Example,(made up numbers)

if Idle current is 30mA @ Plate Volt 200V with -30 Grid
Plot it out on the curve using an 8K load.

Gives Imax of 50ma and Imin of 10ma
So in parallel into the ACTUAL Impedance of 4K I have

Imax 100mA Io 60mA and Imin 20mA...correct
Voltages stay the same so Pout is 2x the single with twice the load
Distortion should be the same?
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Old 27th March 2009, 04:57 AM   #9
nhuwar is offline nhuwar  United States
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Ok ,, I could be wrong but, let go back to simple ohms law. How do you double the load resistance and double the current draw. These 2 are inverse of each other,,,, aren't they???




Nick
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Old 28th March 2009, 06:25 PM   #10
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Quote:
Plot with twice the load resistance and then I can double the currents for what will actually flow at any given grid voltage?
This statement is a bit confusing. You can plot load lines and find a good one for a single section, then put a plate load of half the resistance that you found in your load line (twice the load). Your load line will be correct for either half. Current for the pair will obviously be double what your line for one half indicates. (since there are two)
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