I have a Triplet AC precision panel 4" x 3" Vmtr. model 430C that I've been using for years to measure filament voltage. Nothing melted including the "Shoebox" single 813 rig that I built some yrs. ago (HUZ's page) so I know it works but am not sure if its 1% accuracy is true on 60 cyc. Just found written below the face mask '400 cycles' and in handwritten india ink "1%."
So I hooked up a small 6.3 / 0.3amp fil. xfor and found the following;
7.05 volts on the Simpson reads 6.79 rms on a digital Greenlee. Now I wonder who's right, but the Greenlee does reliably read around 120 vac on my mains which has been verified by pwr. co. - uh, huh, yeah assuming they have accurate voltmeters.
Is there a formula that might apply here assuming the diff. is due to going from 400cyc to 60 and not an innaccurate meter?
Don't tell me it's V * (400/400-60) or 'cos' this or 'sin' that.... heh, heh.
Better yet, Oh I know, it's (7.05 - 6.79) * V