I am currently working on a Philco AM portable Model #53-642, I have replace the selenium rectifier (and the filter capacitors) and I've notice the plate voltage on the tubes is anywhere from 2.5 to 10 Volts higher than the schematic. Although the radio works, I am concerned about inadvertently shortening the life of the tubes.

I am considering installing a 2-Watt 18 Ohm resistor in series with the new rectifier diode to prevent current surge and to drop the B+ down to within specifications. Would this be a good value to use? Or should it be more like 100-150 Ohms at 5 Watts? Thank you in advance for your help.

Hi Mark,
I would not worry too much about the B+ or plate voltage being slightly high. Most schematics will indicate DC voltages as +/- 10% to 20%, so the 2.5 to 10 volts you mention is well within this tolerance. Of more concern is tube filament voltage, you want to keep this between 1.4 and 1.5 volts to prolong tube life. If it is high, you can install a resistor in series with the new rectifier diode as you mentioned. I would use a 5 watt resistor, between 33-47 ohms, to start with. If necessary you can experiment with different values to get your tube filament voltage where you want it.

Poston

:I am currently working on a Philco AM portable Model #53-642, I have replace the selenium rectifier (and the filter capacitors) and I've notice the plate voltage on the tubes is anywhere from 2.5 to 10 Volts higher than the schematic. Although the radio works, I am concerned about inadvertently shortening the life of the tubes.
:
:I am considering installing a 2-Watt 18 Ohm resistor in series with the new rectifier diode to prevent current surge and to drop the B+ down to within specifications. Would this be a good value to use? Or should it be more like 100-150 Ohms at 5 Watts? Thank you in advance for your help.
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