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 JLH output stage
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sajti
diyAudio Member

Join Date: Apr 2003
Location: Százhalombatta, Hungary
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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 20th January 2008, 10:23 AM #2 Jan Dupont   diyAudio Member     Join Date: Apr 2003 Location: Copenhagen, Denmark 6 mA + the Base Current to the output device I would Guess by calculating in my head....... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com
sajti
diyAudio Member

Join Date: Apr 2003
Location: Százhalombatta, Hungary
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

 20th January 2008, 10:32 AM #4 sajti   diyAudio Member   Join Date: Apr 2003 Location: Százhalombatta, Hungary 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
 20th January 2008, 10:45 AM #5 Jan Dupont   diyAudio Member     Join Date: Apr 2003 Location: Copenhagen, Denmark 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....... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com
 20th January 2008, 10:54 AM #6 sajti   diyAudio Member   Join Date: Apr 2003 Location: Százhalombatta, Hungary 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
 20th January 2008, 11:01 AM #7 Jan Dupont   diyAudio Member     Join Date: Apr 2003 Location: Copenhagen, Denmark 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..... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com
 20th January 2008, 11:09 AM #8 sajti   diyAudio Member   Join Date: Apr 2003 Location: Százhalombatta, Hungary 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
sajti
diyAudio Member

Join Date: Apr 2003
Location: Százhalombatta, Hungary
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

Jan Dupont
diyAudio Member

Join Date: Apr 2003
Location: Copenhagen, Denmark
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 ?
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Spare time company (just for fun): www.dupont-audio.com

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