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Old 18th September 2012, 06:00 PM   #1
east electronics is offline east electronics  Greece
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Location: Athens GREECE
Default bias help

in an amplifier like the one shown in the att. i am about to replace obsolete transistors

Also i have to do plenty of metalwork to create space enough to fit them

Question is how i am going to be able to adjust idle for this amplifier ???

here is the

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Old 18th September 2012, 10:57 PM   #2
magnoman is offline magnoman  United States
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I only see the potential to change the current and Vbe of Q009 and Q010 via resistors marked *R019 and *R018 but I suspect you already knew that.

Hope this helps

Last edited by magnoman; 18th September 2012 at 10:58 PM. Reason: typo
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Old 19th September 2012, 12:15 AM   #3
Dave Zan is offline Dave Zan  Australia
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Default Unusual centre driven bias

That is a somewhat unusual bias circuit, what is it from?
I am interested in "centre driven" bias circuitry like this for use in amps with complementary LTPs but it seems unneeded complexity here.
Does anyone know what it is intended to achieve or have any references?
R020 / R022 and R025 / R026 also would seem to set the current.
Perhaps related to power supply noise rejection?
Current thru *R018 and *R019 will be modulated by supply noise.
I will think more if no one has the answer!

Best wishes
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