[Dubis7]

I think I'm actually on the right track with this one as is, but I wanted to get some thoughts from anyone who has more experience than me.

I'm rebuilding a National SW-54 shortwave radio. It's a pretty standard restoration so far, but this set has a few major issues. The cheater cord on the back was physically melted, and the shunt resistor across the rectifier tube was burned in half. As near as I could tell, this was due to the set being run with dead electrolytics for long enough to cause a meltdown. There's a scorch mark on the underside of the cabinet where it failed.

Anyway, I've replaced most of the caps and rebuilt the power supply. I picked up a kit from Hayseed Hamfest and apparently my set is a later revision with some additional .002 uf caps between the antenna inputs and one of the coils. No biggy, I've done the rest and those won't impact a basic power up.

Well, anyway, I got it to come to life for a moment, but it died again just as quickly. Checked under the chassis, and there's two resistors in series. One goes to a ground connection through Pin 1 of the 50C5, and the other acts as a bridge between two of the filter cap sections. The one providing the bridge was smoking and hot to the touch (my finger proves it, oh well) so I measured both. Bridge resistor (looks to be a 1K from the schematic) looks to be in tolerance, but I'm getting some odd behavior from the one going to the 50C5. It measures 1K when the set is cold (should be 15K if I'm reading the schematic right), but I noticed that the resistance dropped to 0 when I applied power.

A dead short to ground would explain the smoking 1K resistor, and probably my dead reception as well. I mostly wanted to know if having a resistor become a dead short when power is applied sounded like something anyone has any experience with.

I'll attach the schematic as well, although it's not a perfect match to my set. On mine there's an additional resistor between the 1K bridge and the 60uf filter section that I can't seem to find on the the diagram, and the resistor that's marked as being in parallel with the C1D section coming off of Pin 1 on the 50C5 is in series with it instead. I'm assuming mine is a different revision since it also has a network that isn't listed here, but I'm no expert.

Since both resistors were getting hot, I have parts on order to replace them. I'm hoping removing that wonky 15K will get me back up and running. I have to believe the meltdown I mentioned previously took that out as well.