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Old 15th October 2004, 08:10 AM   #1
garbage is offline garbage  Singapore
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Question thoughts on 300b operating points with 3k output

hi all

i used formulas from steve bench's site on my operating point for a 300b tube, 3k output transformer, used in a SE amp.

operating point for 300b:
Vp-k: 300V
bias: -59V
Ia: 80mA

the figures are approximately :
Po at 6.77W, 8ohm and 13.53W, 4ohm.
HD2(%) 5.322580645
HD3(%) 3.548387097
HD4(%) 4.35483871

are the above acceptable values, given my operating point?
care to share your 300b operating points?

thanks.

rgds
garbage
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Old 15th October 2004, 09:52 AM   #2
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The OPT Z sounds about right, but why on earth so much 3rd harmonic?
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Old 15th October 2004, 09:55 AM   #3
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Let have a look at the operating points KWY suggests
An intriguing 6S45P direct coupled 300B amplifier
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Old 15th October 2004, 11:54 AM   #4
garbage is offline garbage  Singapore
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Quote:
Originally posted by Geek
The OPT Z sounds about right, but why on earth so much 3rd harmonic?
i've no idea really. i calculated with the formulas on steve's site.

Quote:
Originally posted by Antonio Tucci
Let have a look at the operating points KWY suggests
An intriguing 6S45P direct coupled 300B amplifier
thanks, i read your thread previously.
i noticed he suggested 350V/60mA/5K load with 74V Bias. but that is with 5k load. i am using a 3k load. drawing load line for 5k load and 3k load will differ, resulting in different parameters.
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Old 15th October 2004, 12:43 PM   #5
garbage is offline garbage  Singapore
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Default did some more accurate calculations

i did more precise calculations of the loadline at 300v, -59v bias.

the 300B loadline looks like this:
Click the image to open in full size.

giving values of
Va : 83.63 V
Ve : 474.54 V
Po : 6.37W, 8ohm or 12.73W, 4ohm

Current at 0 volt grid bias
Ia : 152mA

Current at half the quiescent bias voltage
Ib : 109.2mA

Quiescent Current
Ic : 80mA

Current at 1.5 times the quiescent bias voltage
Id : 48mA

Current at twice quiescent bias voltage
Ie : 20.71mA

THD(%) : 4.840429583
HD2(%) : 4.952205309
HD3(%) : 2.309210868
HD4(%) : 3.105356122

calculations taken from Steve's Tube Pages

an excel file of the calculations can be found here:
Attached Files
File Type: zip 300b calculator.zip (2.0 KB, 89 views)
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Old 19th October 2004, 01:33 AM   #6
garbage is offline garbage  Singapore
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Default an update, in case someone has the same question

Click the image to open in full size.
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