[Joeztech]

This morning I discovered that the R102 300 ohm resistor between the 5Y3 cathode and the input capacitor is completely open. It showed signs of having been very hot - any markings on the outside of the resistor are completely burned away. I note that the original Code 121 version was passing about 92mA through the field coil choke (dropped 60VDC and had a DC resistance of 650 ohms). I assume that this Code 125 version power supply has to pass about the same overall DC current so that would say that the R102 would dissipate about 28 Watts! That seems rather high and the original resistor does not look to be any more than about 10W in size.

According to the original Code 121 information the DC volts at the cathode of the 5Y3 is about +300VDC and that is based on having one 20uF electrolytic section at that point before it goes through the field coil choke. The Code 125 version I have has the R102 300 ohm resistor ahead of any electrolytic section and the first electrolytic capacitance it sees is about 35uF with the usual tolerance. So that means that R102 has to absorb some AC energy as well as the DC drop across it.

Any suggestions?

Joe