I am replacing 2 selenium rectifiers with a 1N4007 silicon diode. First 2 in series rectifiers - .630A (federal 1267A) and second 2 in series .540adc (federal 1319A) and need the correct voltage dropping resistor to use in each application?

I would just install the replacement diodes, and see how the voltages wind up. If the are much out of whack, then add the necessary resistor.

It totally depends upon the current, which we can't tell from your post. So, just put in the diodes, and monitor voltages.

The only voltages that are really critical in most radios are filament voltages, especially for battery type tubes. Otherwise the B voltage is very non-critical, except perhaps with fixed bias tubes. Self-bias and grid-leak circuits are non-critical of B voltage.

The resistor will, however, help reduce hum. 50-100 ohms is fairly adequate.

The short answer is: start with a 100 ohm resistor in series. Measure the B+ voltage. Choose another resistor if the voltage is above or below the mfr. spec.

Maybe this helps?
http://w3hwj.com/index_files/RBSelenium2.pdf

Make sure the resistor wattage is at least twice what you calculate. I like resistors to run cooler.

Rich

:The only voltages that are really critical in most radios are filament voltages, especially for battery type tubes. Otherwise the B voltage is very non-critical, except perhaps with fixed bias tubes. Self-bias and grid-leak circuits are non-critical of B voltage.
:
:The resistor will, however, help reduce hum. 50-100 ohms is fairly adequate.
: