Radio Update

The radio is ready to put back together again.  We'll see if all the king's horses and all the king's men can do it.

It's been a bit of an adventure, to be sure.  Old engineering diagrams can certainly be problematic.  But I have been REALLY enjoying myself.  As I said before, it's been quite a long time since I've worked on a "hands on" project like this.  I've had some problems along the way though...

The first problem that I ran into was that I could not, for the life of me, find C14 (Capacitor 14) in the engineering diagram or in the radio itself.  It was just not there.  I asked around a bit on a Philco Radio forum, and was told that that particular capacitor (or condenser, as they call them) was part of the AVC (Automatic Volume Control) circuit, and the radio wouldn't work well without it.  I figured that I could see where the capacitor is on the schematic diagram and I could use that to figure out where it SHOULD be on the radio.

The second problem was that a 50L6-GT tube appears on the schematic, but when I pulled the tube out of the radio, it was a 50C5 tube.  This is a problem because 1) the 50C5 is much smaller and 2) the 50C5 has a different number of pins!  A little research led me to a site that contains spec. sheets for vacuum tubes, and using the diagrams on the spec. sheets, I was able to figure out which pin on the 50C5 tube would match up with which pin on the 50L6-GT tube.  It's not a small difference!

Because of the second problem, it was difficult for me to determine which resistors in the radio matched up with 3 of the resistors on the engineering diagram.  Tracing around the schematic diagram and looking at the engineering diagram, I was able to determine with certainty which resistor was which.

Once the replacement parts arrived, I started pulling parts off of the radio, and suddenly I found C14!  When I checked the engineering diagram again, I found that it was labeled as C9.  Also labeled as C9?  C9.  C14 had been mislabeled on the diagram.

As of last night, I have a nice, clean radio chassis, ready to solder replacement parts into.  I have pulled out mouse-chewed wires, beeswax and paper capacitors, and several resistors.  Once it's all put back together again, I'll check all of the connections and plug it into my dim bulb tester (without the tubes) to check for obvious shorts or other problems.  Hopefully, I won't "let the smoke out" of any of my new parts in the process, but that's what the dim bulb tester is designed to prevent.

I'm probably going to wait to put the tubes into the radio until after my tube tester arrives.  Yes, I bought a 50-ish-year-old tube tester on eBay that is in working condition.  That way, if any of the tubes have shorts, I can replace them BEFORE they destroy anything in the radio.

Once I have good tubes, it will finally be time to see if this 62-year-old radio will again come to life.