I’ve been doing a lot of restoration / repair work lately. Even for those just interested in experimental instruments and synthesizers, a lot can be learned from repairing and restoring radios. Here’s a Zenith trans-oceanic I had in the shop a month ago or so: 
This one is an 8G005 ..The chassis numbers and components indicate is from 1947. It was brought to me completely inoperable. Here’s what the chassis looks like. I only removed the dial because it needed to be “restrung”.
View of tubes and restrung tuning mechanism
REPAIRING THE ELECTRONICS:
So, as with anything I set about carefully examining the electronics. Always LOOK, smell, touch (with power off) before soldering or removing anything. Just one look, and I could see that half the oil containing capacitors were bad. They looked like swollen paper burritos coated in a little wax & dripping oil. Okay so, I started methodically replacing the capacitors. This is a known first step after checkin basics like safety safety safety (frayed cords, etc). Here you can see half of axial oil caps are replaced with new mylar capacitors:
Some of the capacitors are replaced in this photo...
Yes, this is the way the radio was constructed — point to point wiring. After some coffee and a little practice is starts to make sense, and it is best to wire the replacements in the same manner. Circuit boards were unheard of at this time, and everything I fix from this era and earlier looks similar. Yes, it’s ugly, but it works. Here’s the trick — Take a digital photo at EVERY step. Before you replace anything, after you change one part, etc. This allows you a roadmap for your repair. I used to draw that map, but a digital camera at hand makes it so much easier.
The Blue electrolytic caps are for power filtration. The original electrolytics are the big black round cans mounted on the chassis itself. My Electrolytics are small enough to fit in the 1947 chassis comfortably, especially after replacing some oil capacitors with small mylar capacitors (caps must be rated above 150V!!).
Woah, stop for a second. Transoceanics, and a LOT of tube radios of the time can be more dangerous than taking a bath with a hairdryer if there are specific faults:
#1 — This radio has no power transformer! 110 to 220 volts at 15 amps is present throughout the chassis, and is NOT insulated for your protection. Touch the wrong solder blog and POW! So use a probe and keep your fingers behind the multimeter probe’s metal parts. THERE IS NO ISOLATION, and NO FUSE. ONLY POWER UP THIS TYPE OF DEVICE UNDER TEST WITH AN ISOLATION TRANSFORMER AND A FUSE (1 amp a.g. in this case is good) — a variac wouldn’t hurt either, but the iso transformer is a must must must. I use a Sola brand regulating isolation transformer, which is pricey, but all-electronics can hook you up with a basic one for less.
#2 — The metal chassis is HOT — that means that a live current is designed to flow through it. This may seem strange now, but it makes sense for the era. Due to the war, there was not much steel, so transformers were expensive. Instead, designers used vacuum tubes with 115 V heaters to rectify wall current. The resultant designs, which also accepted batteries, had “hot” chassis, so the answer was to seperate the useful high voltage from the chassis with a capacitor, keeping the chassis at only about 1v DC with little current. The designers also placed the chassis inside a wooden case, far enough from fingers to do potential harm, and usually coated with non-conductive paint. However, if that single .47uF Capacitor keeping 100V DC away from the chassis shorts, one could get a shock. I replace it with a UL or CE certified capacitor, like those in good switching power supplies.
A square, grey UL/CE power supply cap is used for safety...
I also added a fuse to this radio to protect the electronics and the user. It’s simple to fit a holder just inside the chassis and wire it between the hot wire and the power switch.
After all the work and 1 replaced tube, this radio outperforms most Transoceanics I have repaired to date. This is a great model — tough and robust. The loctal tubes work well and last a long time, usually not needing replacement.
Finally, this is intended as an overview of what I do, and maybe to give some insights for savvy experimenters. I encourage you to enter the world of radio tinkering, but don’t do it without reading up and making sure you have the right tools.
If you want me to take a look at your vintage electronics or do restoration work for you, contact me through this website! I love doing this sort of work and take great pride in the results. These in-between pictures show some ugly nuts and bolts, but the finished restoration is a thing of beauty.
