Beomaster 5500

9th January 2011

The power amplifier of this receiver was overheating badly so the bias current was checked and found to be greatly in excess of its correct value on both channels. Disconnecting 3P22 returned the conditions in the output stage to normal and it was soon found that the output of the pre-amplifier contained a large amount of high frequency noise. This was coming in through the -12V supply, adding a 100nF 63V capacitor across the B-E junction of 2TR8 (BC557B) in the -12V regulator circuit provided a complete cure. [Beomaster 5500]