WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Yeeeah, electrolytics have a 10% tolerance right?
I looked into switchers, they're cheap and some are adjustable, but most are only good for about 10% more voltage. 5.5v is close, but not quite enough.