Setting quiescent current on beolit 600 - UK Vintage Radio Repair and Restoration Discussion Forum

Nukeybrown · 10th May 2017, 10:15 pm

Does anyone know the procedure for setting quiescent current on the beolit 600 not the thin beolit the older one, im guessing its set by p4 potentiometer but unsure .

crackle · 11th May 2017, 6:51 am

Looking on the Radio Museum there are 4 models of the Beolit 600. 2 of them are the older style, I cant see any adjustment on the schematic for setting the OP transistor bias. But then I am not an expert.

Mike

roffe · 11th May 2017, 10:32 am

It's fixed by two resistors at the bases at 8mA and not adjustable.

'LIVEWIRE?' · 11th May 2017, 11:07 am

Which means, in thory at least, that if the o/p transistors are replaced, the values of the two resistors (2K7 & 47R) should be changed, if neccesary to set the Iq to the correct level. In prctice I suspect it wouldn't be neccesaryalthough temporarily substituting the 47R with a 100 ohm preset, and adusting it to give 8mA then fitting the nearest available fixed resistor might be a good idea.

roffe · 11th May 2017, 4:01 pm

Actually the opposite.
If you need to change the value of the current,always change the upper resistor(the one with the HIGHEST value).
Tweaking the one with the the lowest value creates high changes in base/emitter voltage.
(don't ask me how I know....)

'LIVEWIRE?' · 11th May 2017, 5:27 pm

After I posted my comment, I did wonder about that, Roffe. Using a 4k7 or 5k preset to determine the correct value needed for 8mA Iq would be better for the reasons you stated.

10th May 2017, 10:15 pm	#1
Nukeybrown Heptode Join Date: Jan 2016 Location: Gateshead, Tyne and Wear, UK. Posts: 504	Setting quiescent current on beolit 600 Does anyone know the procedure for setting quiescent current on the beolit 600 not the thin beolit the older one, im guessing its set by p4 potentiometer but unsure .

11th May 2017, 6:51 am	#2
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Setting quiescent current on beolit 600 Looking on the Radio Museum there are 4 models of the Beolit 600. 2 of them are the older style, I cant see any adjustment on the schematic for setting the OP transistor bias. But then I am not an expert. Mike

11th May 2017, 10:32 am	#3
roffe Hexode Join Date: Nov 2003 Location: Linkoping, Sweden Posts: 493	Re: Setting quiescent current on beolit 600 It's fixed by two resistors at the bases at 8mA and not adjustable. Attached Thumbnails

11th May 2017, 11:07 am	#4
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Setting quiescent current on beolit 600 Which means, in thory at least, that if the o/p transistors are replaced, the values of the two resistors (2K7 & 47R) should be changed, if neccesary to set the Iq to the correct level. In prctice I suspect it wouldn't be neccesaryalthough temporarily substituting the 47R with a 100 ohm preset, and adusting it to give 8mA then fitting the nearest available fixed resistor might be a good idea.

11th May 2017, 4:01 pm	#5
roffe Hexode Join Date: Nov 2003 Location: Linkoping, Sweden Posts: 493	Re: Setting quiescent current on beolit 600 Actually the opposite. If you need to change the value of the current,always change the upper resistor(the one with the HIGHEST value). Tweaking the one with the the lowest value creates high changes in base/emitter voltage. (don't ask me how I know....)

11th May 2017, 5:27 pm	#6
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Setting quiescent current on beolit 600 After I posted my comment, I did wonder about that, Roffe. Using a 4k7 or 5k preset to determine the correct value needed for 8mA Iq would be better for the reasons you stated.