pg dump.. issue with when using crontab

Hi folks,

I have a simple script file db :
#!/bin/bash
pg_dump -U postgres prodDB > /var/a/db/$(date "+%Y-%m-%d_%H:%M")-prodDB.dump

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Which works fine when executed manually ( ./db ).. I get a dump file which
is around 1.9 MB

I run this script from the crontab schedueler (crontab -e) :

# m h dom mon dow command
33 04 * * * /var/a/scripts/db

Which appears to executing the script file, but what I get is zero sized
dump files.
So perhaps it is some use access that is limiting crontab, making it not run
as root.

How can I fix this to work with crontab ? I am thinking that I should change
:
pg_dump -U postgres prodDB > /var/a/db/$(date "+%Y-%m-%d_%H:%M")-prodDB.dump

Thank you in advance / Moe