220/240v selector with 230v wall supply

[chocopower]

Hi there.

In my area i use to have 230vAC in wall supply.
The amp in question have a selector for 220 or 240v.

Heater voltage in 240v: 5.9vac
Heater voltage in 220v: 6.6vac

Which is the "safest" option?

Thanks in advance!

[DummyLoad]

either is within 10% of nominal 6.3V and safe.

for longer tube life choose 240V selection.

--pete