It was in a boombox so possibly the transformer was not dimensioned correctly. But the 2 x 40V indeed seem to have been the windings for the power amplifier. In reality 2 x 55V DC means that the STK was downgraded in output power which is no problem.
You can use it for many a +/- 50...55V rail design. Recycling is nice and all but you may feel better by having a known good power amplifier design and the exact right transformer for it.
You can use it for many a +/- 50...55V rail design. Recycling is nice and all but you may feel better by having a known good power amplifier design and the exact right transformer for it.
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To obtain 27.7V and 26V, I think, it is better to use coil B with the intended centre tap. As it is, coil B can deliver 23.7V. This means, it can be used to build a split power supply with a rail voltage of 23.7*square_root(2) - 0.7 = 32.8V peak. Assuming a ripple of 10%, the usable voltage would be 32.8*0.9 = 29.5V. Be aware, more ripple voltage means less usable voltage.
The 2 x 40V AC windings have the thickest diameter and therefor they are the windings for the power amplifier.
P = U x I
P = U x I
Coil B (first post) delivers maximum 13-0-13v. But thanks for rest of the calculations.