[Guest]

I have a Model 118 with a significant steady hum from the moment it is turned on. The electrolytics in the power supply have been replaced but I am not sure if the polarity is correct. There are two 8 mfd caps in parallel with the positive ends connected to each end of the choke coil and a .25 mfd cap the negative ends are coneected to each other and to the positive end of a 10 mfd cap with the negative end connected to ground. Two friends who know more about this stuff than I do suggested that the 10 mfd unit is part of a line that provides negative bias to the 2nd detector and the the driver and should be reversed with the positive side connected to ground. Most of the tubes with the exception of the 42 audio tubes and the rectifier appear to have high plate voltages compared to those indicated in the pages that accompany the schematic. The original cans are in place (disconnected) but do not give me any insight as to polarity. Thank you for any insight you can provide.