JLH output stage

sajti · 20th January 2008, 10:18 AM

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

Jan Dupont · 20th January 2008, 10:23 AM

6 mA + the Base Current to the output device I would Guess by calculating in my head.......

sajti · 20th January 2008, 10:28 AM

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

sajti · 20th January 2008, 10:32 AM

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

Jan Dupont · 20th January 2008, 10:45 AM

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.......

sajti · 20th January 2008, 10:54 AM

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

Jan Dupont · 20th January 2008, 11:01 AM

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.....

sajti · 20th January 2008, 11:09 AM

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 · 20th January 2008, 11:14 AM

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 · 20th January 2008, 11:26 AM

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 ?

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, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

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, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

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, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
3C24 in a SE output stage - output transformer impedance recommendation !!!	aldovan	Tubes / Valves	15	6th September 2008 10:18 AM
preamp output stage resistor from output to V- ? ?	Bernhard	Solid State	4	19th October 2007 02:55 PM
Output stage biasing, with the driver stage	andrew_whitham	Tubes / Valves	0	19th May 2007 11:14 AM
Adding secondary of output transformer into cathodes of output stage ? Eico ST-70	freddymac406	Tubes / Valves	3	21st April 2007 06:15 PM
TV Horzontal Output Transistor for output stage..?	ronybc	Solid State	46	10th October 2005 02:26 AM


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

20th January 2008, 10:32 AM	#4
sajti diyAudio Member Join Date: Apr 2003 Location: Vác, 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, 10:54 AM	#6
sajti diyAudio Member Join Date: Apr 2003 Location: Vác, 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, 11:09 AM	#8
sajti diyAudio Member Join Date: Apr 2003 Location: Vác, 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

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read