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Old 20th January 2008, 10:18 AM   #1
sajti is offline sajti  Hungary
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Default JLH output stage

I found this output stage in JLH's book. But something is strange for me: What is the current of MJE15033s, if the output stage has 100mA bias?

sajti
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Old 20th January 2008, 10:23 AM   #2
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6 mA + the Base Current to the output device I would Guess by calculating in my head.......
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Old 20th January 2008, 10:28 AM   #3
sajti is offline sajti  Hungary
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Quote:
Originally posted by ACD
6 mA + the Base Current to the output device I would Guess by calculating in my head.......
And in this case what is the current of the BDs?

sajti
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Old 20th January 2008, 10:32 AM   #4
sajti is offline sajti  Hungary
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My calculation is the following:

The current over R3 is ~6mA, due the output devices are open.But the current over R5 must be ~6mA as well. Because if it less, than the MJE-s are switched off. So I think that the current over the MJEs is equal with the base current of the output devices. Is it OK?

sajti
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Old 20th January 2008, 10:45 AM   #5
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You have to take the BD's into the calculation...
I have never tried this output stage, but the BD's can feed the Bases of the MJL's directly.......
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Old 20th January 2008, 10:54 AM   #6
sajti is offline sajti  Hungary
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Of course, but not 6 pairs of MJLs for 2ohms... So I think that I will try to reduce R3 and R4 to 22ohm, to get bias for the MJEs.

sajti
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Old 20th January 2008, 11:01 AM   #7
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Why ??
Only result would be to drive the driver and predriver harder ??
The total Base Current to 6 MJL's at 100mA idle would be app. 20 mA. That would be total app. 26 mA with R3=100R but 47mA with R3=22R.....
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Old 20th January 2008, 11:09 AM   #8
sajti is offline sajti  Hungary
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I plan to use it with valve VAS, so I need triple darlington to get high input impedance.
I have lot of MJE15032/33, but I was not able to select NPN/PNP pairs, because the '33s have much higher B. So I try to find output stage with same polarity driver, and output

sajti
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Old 20th January 2008, 11:14 AM   #9
sajti is offline sajti  Hungary
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Quote:
Originally posted by ACD
Why ??
Only result would be to drive the driver and predriver harder ??
The total Base Current to 6 MJL's at 100mA idle would be app. 20 mA. That would be total app. 26 mA with R3=100R but 47mA with R3=22R.....
Yes, but the base current of the output devices is not well defined. And the lower value resistor result faster switch of for the output devices. With 100ohms, and 6 pairs the output stage will be 6 times slower..

sajti
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Old 20th January 2008, 11:26 AM   #10
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Quote:
Yes, but the base current of the output devices is not well defined. And the lower value resistor result faster switch of for the output devices. With 100ohms, and 6 pairs the output stage will be 6 times slower..


The Base Current are as well defined as on all other transistors ?
Hfe 25 to 75.....
What do yoy meen by slower ?
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