If a bridged amplifier(s) has 39 db gain ......

In electronics dB (as opposed to dBV, dBu, dBm) is a always refering to a notional power ratio, even when not talking about power, which means for current and voltage you square the ratio first, and sometimes you need to be careful to explain if you are talking power, voltage or current.


In RF systems with 50 ohm impedance everywhere then power/voltage/current gains are identical expressed in dB.