World Audio Designs (WAD) 300b Stereo

This amplifier is a clone of the original WAD 300b stereo amplifier. It was ninth workshop of repairs, as valve failure had taken out two cathode resistors. This version had been made with two 6D22 damper diodes for slow start and rectification and the owner was nervous about the top caps, which carry 550v, a potentially lethal voltage.

So we took the opportunity to convert the amp to solid state rectification and I installed a slow start module, to mimic the functioning of the valve rectifiers. We also lowered dissipation as the owner was keen to use Mesh Plate 300b valves, which don’t like to dissipate much more than 24 watts.

So how does the solid state rectification change the sound? I would describe the change as a faster sound with more low level detail apparent, so all in all a small increase in perceived sound quality.

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The slow start module can be seen in the middle bottom of the above photo.