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Old 27th May 2012, 01:39 PM   #1
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Default amplifier biasing help

hi
i have replaced TIP35/36C blow out put stage trasistors from Focal amp and replaced with 2SC5200 pairs.

Now there is a REFERENCE POINT and BIAS CHECK point. The voltage across all four channels is 2mV to 80 mv.

VCE= 30.6 volt for all

VBE= 0.35V to 0.55 Volt ?

Any guidance how to adjust bias before i blow them out again.
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Old 27th May 2012, 02:20 PM   #2
AndrewT is online now AndrewT  Scotland
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The question is back to front with the action.

You ask before you power it up !!!
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Old 27th May 2012, 02:24 PM   #3
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No. Actually its second replacement, the yesterday replacement were all well before i put a bridged load on it.

so yes i am asking before powering it up before second time. But i am using series bulbs with the power supply just in case.:-)
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Old 27th May 2012, 02:37 PM   #4
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Quote:
Originally Posted by muddasirwaheedmalik View Post
hi
i have replaced TIP35/36C blow out put stage trasistors from Focal amp and replaced with 2SC5200 pairs.

Now there is a REFERENCE POINT and BIAS CHECK point. The voltage across all four channels is 2mV to 80 mv.

VCE= 30.6 volt for all

VBE= 0.35V to 0.55 Volt ?

Any guidance how to adjust bias before i blow them out again.
TIP 35 is an NPN whereas TIP36 is PNP inferring a complementary pair. 2SC5200 is NPN, It would suggest to me that you need a PNP to match the replacement of the TIP36.The correct complement for the 2SC5200 is a 2SA1943
Cheers / Chris

Last edited by Chris Daly; 27th May 2012 at 02:43 PM.
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Old 27th May 2012, 02:48 PM   #5
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just forgot to mention though in my earlier post. yes indeed it 2SA5200 was matched with 2SA1943, and tried to match within 5% of VBe, not sure of hFE though.

Biasing ? VBE ? HELP?
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Old 27th May 2012, 03:06 PM   #6
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Quote:
Originally Posted by muddasirwaheedmalik View Post
just forgot to mention though in my earlier post. yes indeed it 2SA5200 was matched with 2SA1943, and tried to match within 5% of VBe, not sure of hFE though.

Biasing ? VBE ? HELP?
Data sheet here: http://www.fairchildsemi.com/ds/FJ/FJL4315.pdf
Cheers / Chris
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Old 27th May 2012, 03:09 PM   #7
DF96 is offline DF96  England
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Have you tried circuit fault-finding to discover why they blew?
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Old 27th May 2012, 05:37 PM   #8
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accidental short circuit at output while trying to put an OP transformer. :-(
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Old 27th May 2012, 08:44 PM   #9
DF96 is offline DF96  England
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OK, so there is not a fault to trace unless the output transistors took something else with them when they died.
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Old 27th May 2012, 09:22 PM   #10
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Quote:
Originally Posted by muddasirwaheedmalik View Post
No. Actually its second replacement, the yesterday replacement were all well before i put a bridged load on it.
:-)
A bridged load needs to be twice the none bridged load.
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