The mains voltages in my neighborhood seem to range from a low of 120v to a high of 125v, but seems to hang out most often in the 122-125 range. So, I used my variac to see what happens to filament voltage levels with mains voltages of 120v, 122.5v, and 125v. I can't seem to help myself, I'm a compulsive tweaker...
![Grin ;D](https://forum.bottlehead.com/Smileys/default/grin.gif)
I have a variety of datasheets and found lots of online discussions that talk about voltage tolerances for tube filaments for lots of tubes except the 5AR4 rectifier that I'm using. All of the datasheets I have found merely state 5.0v but I'm measuring more than that in my build. Does the "typical" window of +/- 10% apply here as well? Will the tube last longer in the long run with a +/- 5% window? My specific tubes are NOS Mullard f31 tubes.
I made a voltage chart and attached it below. Should I leave the rectifier heater as is, or is it better for the longevity of the tube to insert a 0R1 resistor in series that will bleed off 0v19 and shift the heater range down to 4.97v to 5.19v?
Thanks for the perspectives!