Sugden A48 MkII
The Sugden A48 MkII was noted for it's 'heavy-duty' retro approach paralleling meaty TOP3 devices (100V, 25A, 90W) and reverting to AC output coupling, the output capacitor being double the value of the main smoother. This arrangement, with a relatively low quiescent current, was intended to cope with the demands of low impedance loads.
Respected by many, drawbacks, apart from the inclusion of high-voltage high-value electrolytics, included the transformer having two secondaries (one for each amplifier) which, on occasion, proved problematic when seeking a replacement, and the Zobel / Boucherot network being placed after the output relay. This should be taken to the output cap's +. Upgrading the smaller transistors with low-noise types (together with the input and feedback resistors) in line with the 2N5550's rating (140V, 100MHz) and paralleling the electrolytics with polycarbonate types will improve. Note the position of the AC clamping, which perhaps could be replaced by protection at the input.
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