No problem, that will be fine as is. Your line voltage varies more than that.
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0.2V extra will cause the tubes to live shorter. You could use a small value (but rated for the current) series resistor per filament. Best would be to test with actual 5A load how much Volt it measures under load. Noise won't be an issue IMO. You could also rectify to DC and regulate the voltage to 6.3V DC for the preamp/driver tubes and small value series resistors per filament of the power tubes (if any).
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See post #2 in this thread:http://www.diyaudio.com/forums/tubes-valves/237405-why-6-3v.html I should have said .2 VOLTS in post #4.
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You can possibly make a case that an extra 0.2v on the heater will shorten tube life, but by how much? That is only 3% off nominal, the tube is happy within 10%. I have been in electronics now for over 60 years, and in that time I have seen few open heaters. That is the last thing I consider a weak point in a tube.
The heater might boil off a few more electrons from the cathode, but really, this is a guitar amp - or at least an instrument amp - and in such, the power tubes will wear out normally way before the heater will go. And 12AX7s and similar tubes normally will run for decades before wearing out. Ones that fail sooner than that usually go microphonic or have shorted elements, which are not related to heater. besides, if I get 20 years from a 12AX7, and I subtract 3% from that, that is six months.
The heater might boil off a few more electrons from the cathode, but really, this is a guitar amp - or at least an instrument amp - and in such, the power tubes will wear out normally way before the heater will go. And 12AX7s and similar tubes normally will run for decades before wearing out. Ones that fail sooner than that usually go microphonic or have shorted elements, which are not related to heater. besides, if I get 20 years from a 12AX7, and I subtract 3% from that, that is six months.
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