Centre tap transformer unknown rectifier citcuit
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Figure 1. Redrawn schematic.

It looks like you have two centre-tapped secondaries with full wave rectification on each. This wouldn't be unusual other than winding 'b' has a lower output voltage so I've marked the lower DC output '32 L' and the higher one as '32 H'. This in turn makes D3 very unusual.

The only reason for this that comes to mind is that D3 will prevent a high load on 32 H from stealing power from the 32 L line but can supply the 32 L line when power is available.







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