7V is outside the 6.3V +/- 10% range of acceptability specified for vintage tubes, and well outside the 5% spec of many current production types.
Why would it be ok specifically for a Champ?
Smaller PTs tending to have poorer regulation maybe?
Thanks - Pete
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tubeswell wrote:Each pair of 1R||1R losing 0.7A and dissipating 0.25W. By my reckoning = (0.35V/0.5R)x0.35V = 0.245W
That's absolutely correct, anyway I'd go for the initial current (when heaters are cold and their resistance is lower) when choosing the wattage of those dropping resistors, and then use a good safety factor (they have a peak current at the beginning, then they run with a continous current flowing through them, in a warm/hot environment), in order to make them work with a low dT compared to the surrounding.
