[sven_swe]

Hi experts!

I just got hold of a German Neuberger RPM370/1 valve tester that has a selenium rectifier as original. This is for the negative grid voltage in ranges of 5, 10, 50 and 100V with a rheostat for fine adjust.
The section for 100V(110V) has been replaced before by someone with a 1N4007 diode since that section seems to be dead. I can notice some "flickering" when in the 5 and 10V range so it seems that this one is about to give up and I would like to change it.

My question is how to get about to replace this selenium rectifier correctly. I have read that 100-200Ohm high wattage resistor is often used in series with a diode to limit current surge and to compensate for the voltage drop. I do not know what the voltage drop "was" before since a section has already been replaced with one diode but without the resistor.

Would a 1N5408 diode with a series resistor of about 100Ohm 5W be sufficient as a replacement for each section? Which side of the diode is preferred to have the resistor?

I have attached an image of the rectifier and schematics.