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Old 6th May 2009, 05:21 AM   #1
Jeb-D. is offline Jeb-D.  United States
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Default ThermalTrak transistor application.

Balancing current in PP amplifiers. What do you think?

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Old 6th May 2009, 07:00 AM   #2
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Great use of a Thermaltrak!

Same, same but different :

http://www.diyaudio.com/forums/showt...05#post1613405

For a "normal" PP I would substitute the cathode resistor(above the diode) with a CCS as to make both tubes having CCSs at their cathodes.

Also Audiodesignguide has something alike at his site.
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Old 6th May 2009, 09:42 AM   #3
Arnulf is offline Arnulf  Europe
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This assumes ideal (matched) output tubes that don't 'age' differently through use ?
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Old 6th May 2009, 09:52 AM   #4
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Quote:
This assumes ideal (matched) output tubes that don't 'age' differently through use ?
No, the rightmost tube(slave) will get the same current as the left(master). This due to the currentmirror configuration.
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Old 6th May 2009, 02:57 PM   #5
JoshK is offline JoshK  Canada
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Does this keep them in strict class A?
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Old 6th May 2009, 03:04 PM   #6
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Nice app!

But the transistor current is not automatically the same as the diode current. They will track, but you need something more to make sure they are the same.

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Old 6th May 2009, 04:04 PM   #7
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Hey Jan,
As you see in my SEPTOR schematic there are resistors below the transistors. This way you can finetune tracking.
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Old 6th May 2009, 05:30 PM   #8
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I am fairly sure the thermaltrak diode is NOT the same as the
bipolar's emitter. And I'm not sure why it was done that way.
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Old 6th May 2009, 05:54 PM   #9
Jeb-D. is offline Jeb-D.  United States
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Quote:
Does this keep them in strict class A?
No, it just balances current between the two. Could be used for class A or AB.

Quote:
For a "normal" PP I would substitute the cathode resistor(above the diode) with a CCS as to make both tubes having CCSs at their cathodes.
Good idea. I just used a resistor so that it could be used for class AB also. Thanks for the link to the Septor schematic. Have you had good results with the current mirror? I'd think it provides good DC balance regardless of signal amplitude. Opposed to using trimmer methods, which will only balance DC at idle.

Quote:
But the transistor current is not automatically the same as the diode current. They will track, but you need something more to make sure they are the same.
A resistor will be added to the diodes cathode and the BJT's emitter.
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Old 6th May 2009, 05:58 PM   #10
Jeb-D. is offline Jeb-D.  United States
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Quote:
I am fairly sure the thermaltrak diode is NOT the same as the bipolar's emitter. And I'm not sure why it was done that way.
You may be right. I ordered the parts to give it a go. I'll provide some data when done.
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