Philco surgery

The repair parts came in on Friday, so Saturday I got the soldering iron out and proceeded to get those bad parts out of there. First were the capacitors across the line. One was already blowed up, so out came the second one.

As you can see, I pulled the one still there away from the terminal strip to show the wax it left behind. That cap was not long for this world. Here's the replacement.

Here are the original "blowed up" cap, the new replacement, and the other cap about ready to go. You can see printed on the new cap all sorts of regulatory agency approval markings from UL, CSA, VDE and many others. These caps are specifically designed for being placed across the AC line and if they fail will fail safely (not go BOOM). Now the new safety caps are in.


You can see another cap that was replaced, the white braided thick "wire" is actually a power resistor, and you can see what it did to the old capacitor. Nice burn marks.

And now you can see a recurring headache that popped up throughout the re-cap process. The new parts are so much smaller than the originals that in many cases the leads aren't long enough for the parts to go in the same positions.

Now that I had the radio relatively safe, I wanted to check the bias voltages on the output tubes. I suspect that the open bias resistor I found earlier would cause a problem, and it did. Instead of -20V bias on the 7B5 grids I had 0. So instead of a plate voltage of 295, the tubes were drawing much more current than they should have and the plates were down to 220. Very surprised something didn't melt in there.

The next step was to replace every resistor and capacitor in the output stage, as the resistors that hadn't opened were drifting way up in value.

After all that was done, the bias was checked again and it was almost dead on -20V. Plate voltages were up around 310V, a little high but OK, those tubes took quite a beating and are probably very weak now.

That was enough for Saturday, by this time the radio was playing again. Sunday the rest of the capacitors got replaced. These were a little deeper in the chassis, and some surprises were lurking as well.

A "resistor to nowhere". Finally everything was done.

I did not reinstall the wiring to the phono socket because it's too crowded in that area and I never foresee using a phonograph with this.

Now playing on the bench. There's still a couple of minor issues to take care of. The tuning capacitor is dirty so there's much noise when tuning the shortwave bands, the calibration is also off by a bit. But the AM section sounds OK.