Satellit 2000 Audio Circuit Repair

The audio output quality of the Satellit 2000 is very good as one would expect, and on this Grundig radio, you get independent bass and treble controls, and independent loudspeakers. The actual power output to the loudspeaker varies depending upon the circuit receiving power from batteries or mains. Repairing the audio output stage is simple as it is a straightforward design.

The final output is through transistors T24 (AD161), and T25 (AD162) in a common-emitter push-pull configuration. This is an output transformer-less (OTL design), and instead there is an output capacitor C618. T23 (AC121S) drives these transistors, which together with T22 form the basis of zero-crossover distortion adjustment (preset R625).

AD161 (NPN) and AD162 (PNP) are germanium transistors in a SOT-9 package. These transistors usually come as a matched pair for the push-pull stage. If you find that the sound is low and crackling, then these germanium transistors are usually the first to suspect. Luckily, they are still available online so replacing is not an issue these days.

The AC121S is a PNP germanium transistor in a metal tube case, and these can fail sometimes. You will likely find this attached to the heatsink as well and it is worth checking.

This Grundig radio has a 6 mA link (JC) on the collector side, and if that goes open, then there will not be any sound from the radio, hence this is worth checking if your radio goes dead and you are trying to repair it.

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