biasing or quescient current setting

djronbxs · 11th August 2006, 07:10 AM

Hi,

I have an amplifier and has a pair of (2sc3182 & 2sa1265) which are bipolar transistors, can someone help me how to set the best quescient current for them ? the brand of the amplifier I have is SILVER which now this company is ONKYO, I dont have schematics for it !

thanks
ron

AndrewT · 11th August 2006, 07:41 AM

Hi,
it depends very much on the design and the heatsink dissipation capacity.

More Iq means higher case (Tc) and junction (Tj) temperatures.
Higher temperatures reduce the safety margin before blowing up your output stage.
Go easy, and don't be tempted to experiment with high temperature heatsinks (Ts) without the technical information to support your decisions.

djronbxs · 11th August 2006, 12:51 PM

is there a safely or basic quescient current ? I read that it is from 50mA to 100mA. Can I draw a load line for my output transistor and set the resulting current as my quescient current ?

thanks
ronald

AndrewT · 11th August 2006, 03:06 PM

Hi,
load lines belong to Tube (valve) design.

50mA will cause a lot of heating from each output device.
Do not guess and hope! You might destroy your output stage.

anatech · 11th August 2006, 11:38 PM

Hi Ronald,
The normal bias current for production amplifiers will lie between 10 and 30 mA. Most falling in the 15 ~ 20 mA range. Mosfet designs will run 50 ~ 100 mA.

Harmon Kardon ran very hot and had larger heatsinks. It ran a higher bias current.

You are completely safe setting your bias current somewhere between 15 and 20 mA per device. Distortion will not decrease by running the unit any hotter.

-Chris

11th August 2006, 07:10 AM	#1
djronbxs diyAudio Member Join Date: May 2006	biasing or quescient current setting Hi, I have an amplifier and has a pair of (2sc3182 & 2sa1265) which are bipolar transistors, can someone help me how to set the best quescient current for them ? the brand of the amplifier I have is SILVER which now this company is ONKYO, I dont have schematics for it ! thanks ron

11th August 2006, 07:41 AM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, it depends very much on the design and the heatsink dissipation capacity. More Iq means higher case (Tc) and junction (Tj) temperatures. Higher temperatures reduce the safety margin before blowing up your output stage. Go easy, and don't be tempted to experiment with high temperature heatsinks (Ts) without the technical information to support your decisions. __________________ regards Andrew T.

11th August 2006, 03:06 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, load lines belong to Tube (valve) design. 50mA will cause a lot of heating from each output device. Do not guess and hope! You might destroy your output stage. __________________ regards Andrew T.

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11th August 2006, 12:51 PM	#3
djronbxs diyAudio Member Join Date: May 2006	is there a safely or basic quescient current ? I read that it is from 50mA to 100mA. Can I draw a load line for my output transistor and set the resulting current as my quescient current ? thanks ronald

11th August 2006, 11:38 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Ronald, The normal bias current for production amplifiers will lie between 10 and 30 mA. Most falling in the 15 ~ 20 mA range. Mosfet designs will run 50 ~ 100 mA. Harmon Kardon ran very hot and had larger heatsinks. It ran a higher bias current. You are completely safe setting your bias current somewhere between 15 and 20 mA per device. Distortion will not decrease by running the unit any hotter. -Chris

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