Studio Reference Amplifier - Page 40

leonatax · 8th December 2011, 08:09 AM

This is my SR50 and SR200

apexaudio · 8th December 2011, 10:39 AM

Quote:

Originally Posted by leonatax

Apex I need your help, the BF421 is geting hot on idle on my RS50 what can be the problem?

Nice work, BF421 must be hot, but you can replace BF421 with resistor like in SR200.
Regards

leonatax · 8th December 2011, 01:27 PM

Thanks

apexaudio · 8th December 2011, 01:34 PM

Quote:

Originally Posted by apexaudio

Nice work, BF421 must be hot, but you can replace BF421 with resistor like in SR200.
Regards

Q7 on SR50 is BF420 not BF421.

leonatax · 8th December 2011, 01:49 PM

The problem is that q10 BF421 is geting hot not q7

apexaudio · 8th December 2011, 06:32 PM

Quote:

Originally Posted by leonatax

The problem is that q10 BF421 is geting hot not q7

Ok, all BF420/421 must be hot 12mA x U rail is about 600mW per BF. Replace R16 and R17, use 2k2 instead 3k3 for 6mA thru BFs or 2k7 for 8mA and temperature of BFs will decrease.
What is PSU rail voltage for your SR50?

leonatax · 9th December 2011, 05:02 PM

Rail voltage is +-40 vdc 6amps and BF421 is hot even if nothing is conected to amp

leonatax · 9th December 2011, 05:05 PM

I use regulated psu with 2 pairs of tranis

AndrewT · 9th December 2011, 07:58 PM

12mA @ 40V is almost half a Watt. That is hot!

apexaudio · 9th December 2011, 09:41 PM

Quote:

Originally Posted by leonatax

Rail voltage is +-40 vdc 6amps and BF421 is hot even if nothing is conected to amp

It's OK VAS work in class A, all BFs must be hot without input signal and output load, and you can measure voltages on 100R resistor (about 1,2V for 12mA) and measure offset on amp out (about 1mV) if not something is wrong.

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8th December 2011, 01:27 PM	#393
leonatax diyAudio Member Join Date: Oct 2011 Location: Moldova	Thanks

8th December 2011, 01:49 PM	#395
leonatax diyAudio Member Join Date: Oct 2011 Location: Moldova	The problem is that q10 BF421 is geting hot not q7

9th December 2011, 05:02 PM	#397
leonatax diyAudio Member Join Date: Oct 2011 Location: Moldova	Rail voltage is +-40 vdc 6amps and BF421 is hot even if nothing is conected to amp

9th December 2011, 05:05 PM	#398
leonatax diyAudio Member Join Date: Oct 2011 Location: Moldova	I use regulated psu with 2 pairs of tranis

9th December 2011, 07:58 PM	#399
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	12mA @ 40V is almost half a Watt. That is hot!