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Old 8th November 2005, 02:25 AM   #1
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Default Tube Load Line

Hi All.
Picture below is the load line i draw for EL84. I plot it on 250V and 40mA in triode mode. Am I draw it correctly?
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File Type: jpg jj-el84 plate characteristic.jpg (81.0 KB, 400 views)
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Old 8th November 2005, 02:41 AM   #2
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those look like pentode curves to me
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Old 8th November 2005, 02:46 AM   #3
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Yes, You're right it's a pentode load line. But since that's what i got from Data sheet (I used JJ-EL84), that's why i confused to decide the right bias voltage.
Do you know how create a Triode loadline from pentode?

thanks and regards
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Old 8th November 2005, 03:06 AM   #4
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It's difficult to make a pentode into a triode load line except when you have curves at Vg1=0 and varying Vg2. And even then, you can oly derive the Vg1 = 0 curve. Fortunately, triode curves for the EL84 are easily available. Look at the Mullard data sheet, available at the ubiquitous and invaluable Frank's Electron Tube page.
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Old 8th November 2005, 05:28 AM   #5
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Sy,

FYI, I believe someone else is currently using the new avatar you have chosen and has been for quite some time.
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Old 8th November 2005, 06:20 AM   #6
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Unless it's Mick Abrahams, I'm not changing!
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Old 8th November 2005, 07:11 AM   #7
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Hi SY and All,
I found Mullard datasheet... yes there's drawing for triode... I also tried to draw with Plate Voltage 250V Plate Current 40mA at load 5k Ohm. Unfortunately i can't see max voltage since it off scale. the load line is on the red line while green line is max. plate current (65mA).
Now, Am I draw it correctly?
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Old 8th November 2005, 12:31 PM   #8
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The blue line is the correct load line for the EL84 triode SE with a 5K resistive load. The red line would correspond to a transformer load, assuming an ideal transformer.
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Old 8th November 2005, 02:50 PM   #9
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Thanks for your Info SY...

If i set up circuit to follow the red line, what about the max current limit? I marked green line as Max current limit (65mA).
Does it mean that's a bad load line because already reach max current before bias get 0 Volt or I still can use it as long as i don't drive it near max current....?

Thank you for your explanation and others opinions are welcome too....

best regards
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Old 8th November 2005, 03:42 PM   #10
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I wouldn't worry too much about the max current since your average current will be well below that. You might want to plot max dissipation on those curves to see if your loadline stays below it (on average).

Off the top of my head, 5K and 250V is pretty safe for an EL84- in my little amp, I'm running them with 300V in a push-pull circuit with 8K plate-to-plate. That corresponds to a 2K load single-ended, which is tougher than your load. My tubes seem to be perfectly happy.
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