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Leon Crampin · 27th Feb 2020, 7:50 pm

hfe is very dependent on collector current, so consult the data when checking. These sets do not show exactly half the supply voltage at the speaker coupling capacitor, but the voltages shown on the diagram are pretty close if you correct for 240V mains. The amplifier supply is usually about 17V in normal UK mains operation.

If you read the voltages from the circuit, be careful to interpret correctly the dotted rectangles around the values. These give the measuring conditions.

The electrolytics generally are suspect if made by our friends ERO. You could usefully check the bootstrap capacitor.

You did common the 3 negative connections to the original smoothing capacitor - I hope.....

Leon.

27th Feb 2020, 7:50 pm	#8
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,870	Re: Grundig Concert Boy 1100 (again) hfe is very dependent on collector current, so consult the data when checking. These sets do not show exactly half the supply voltage at the speaker coupling capacitor, but the voltages shown on the diagram are pretty close if you correct for 240V mains. The amplifier supply is usually about 17V in normal UK mains operation. If you read the voltages from the circuit, be careful to interpret correctly the dotted rectangles around the values. These give the measuring conditions. The electrolytics generally are suspect if made by our friends ERO. You could usefully check the bootstrap capacitor. You did common the 3 negative connections to the original smoothing capacitor - I hope..... Leon. Last edited by Leon Crampin; 27th Feb 2020 at 7:59 pm.