can diods be responsible for loss of 0.5V in alternator?

[kbogach at comcast.net]

Two 110Ah alternators have same voltag regulators (different batch 
though)  and one ouputs 14.8 V and another 14.3.    I don't remember how 
details of the diod bridge schema and how it works.   If someone is on 
top of this stuff,  can you tell me if diods can cause the loss of 
0.5V?    I have the regulator (brand new)  and bad soldering inside 
(visually not detected when I took the alternator apart for bearing 
replacement)  on the list of culprits.   Any better ideas?

Thanks.
Konstantin.