Beocenter 3500

23rd May 2011

Overheating of the output transistors of either channel should draw attention to resistors 480 and 559 (1.8k) as they are often found to be high in value. The bias current presets 481 and 561 (250R, replace with 220R or 470R with an extra 470R resistor in parallel) also drift so ideally all these parts should be replaced together, along with resistors 482 and 560 (560R) if they are out of tolerance. 20mA of quiescent current, measured at the collector of the upper 2N3055 output transistor, is a good setting to aim for, repeat the adjustment after 30 minutes operation as the current may drift upwards from its “cold” value. The Beomaster 3000 and Beomaster 3000-2 use the same circuit. [Beocenter 3500, Beomaster 3000, Beomaster 3000-2]