How close is "close enough" with a PT?

[Ripthorn]

I just got myself a 12.6V transformer to run the heaters of my tubes in series, but when I measure the output, I am measuring 14.5V. I was wondering if this is close enough (my tubes specify 6.3V +/-.3V) or if I should try to get it closer. If I need to get closer, what is the best way to do so? Would it just be a resistor to drop the 2V or is there a better solution?

[Wayne]

Your 12.6V transformer will put out more than 12.6V if it has no load other than your voltmeter. Once you start providing enough current to heat your tubes, the voltage will fall. If it still is too high, you can put a resistor in each lead to drop some voltage.

Hope this helps.

W

[Ripthorn]

That is exactly what I needed to know. I will make sure to check the voltage as soon as it is hooked up to the heaters and adjust accordingly. Luckily, the heater current seems very predictable.

[Wayne]

Not only that, but heaters are fairly forgiving as well. If you run your tubes much over the rated heater voltage for their entire life, their life will be shorter. If, however, you run them over the rated voltage for a few minutes, you will probably not have done any harm. IMO.

W