Help Luxman L-55a bias adjust...

[bonzzo]

Help Luxman L-55a bias adjust... Thank u.
Best regards

 

[ecluser]

Do you have a schematic or service manual by any chance?

 

[bonzzo]

yes, but I do not have the value of the bias settings. Thank you. Bonzzo

 

[vibroverbus]

Try on the Yahoo luxman group - http://tech.groups.yahoo.com/group/luxman/

 

[ecluser]

If you don't have access to sophisticated test equipment, measure the DC voltage across each emitter resistor in the output stage. If those resistors are properly calibrated, this voltage should be 13~26 mV at room temperature. Since your emitter resistors are low (0.1 Ohm), it seems that this value was dictated by efficiency rather than the transistor's parameters. I would adjust the bias to have no more than 5mV across each emitter resistor in first instance. This corresponds to a bias current of 50mA.

 

[bonzzo]

Ok...please, help me in this photo

 

[OverLoad]

It's hard for me to tell from your picture but it looks like your measuring points are directly from emitter to emitter of the output transistors which is fine. If not, then use the points I've shown in the attached picture. If your looking to achieve 50mA of bias current then measure across the emitter resistor pairs of each channel and set each bias pot for 10mV's at those points. Personally I think 50mA's might be a "little" hot for this amp. Without knowing for sure I'd probably set it for 35-40mA, which would mean a 7-8mV measurment across the emitter resistor pairs.

SEE THE ATTACHED PICTURE

 

[ecluser]

They are the same points. The picture doesn't show, but there is a large heat sink in this amp. I don't think it would overheat at 50mA, but as I said, it would be the maximum bias current for a first trial.

 

[OverLoad]

As I mentioned, it was hard to tell from his photo if indeed he was using the transistor emitters. I described to measure across the emitter resistors with a depiction to leave ZERO doubt. Yes of course they are the same points "electrically".

 

[bonzzo]

I understood. I measure across the emitter to emitter. Now I have 13mv.
Can you tell me that regulate the red variable resistor? Thank you very much. Bonzzo

 

[bonzzo]

up...

 

[Susurus]

I have a non-running one of these. Looks beautiful in champaign gold. Lettering is inset too.