Heterodimeric electron transfer flavoprotein that accepts electrons from trimethylamine dehydrogenase (PubMed:7798207). It transfers the electrons to the main respiratory chain via ETF-ubiquinone oxidoreductase (ETF dehydrogenase) (Probable). EtfB binds an AMP molecule that probably has a purely structural role (PubMed:7798207). Heterodimer of an alpha and a beta subunit. Belongs to the ETF beta-subunit/FixA family.