Have you ever restored one of those late 40’s or early 50’s sets, and despite having checked or replaced everything above and below; the set is intermittent, "staticy", weak, won’t align, or all of the afore mentioned combined? Your problem can probably be found in the if transformers. This is not confined to AM sets, but FM sets, and AM/FM combinations as well. Some of the 40’s Hallicrafters S-38 series sets are often affected and can drive a novice technician (and sometimes an old pro) insane. Don’t dispair, there is a solution, and with a steady hand and the proper tools; you can repair those troublesome transformers. To do the job you will need the following: good lighting, a magnifier, small forceps, soldering iron, small flat blade screwdriver, bench vise, hand drill and assorted bits, small wire cutters, and a felt tip marking pen. Each transformer will require at least two replacement capacitors. For 455 K Hz use 100 pF mica or ceramic capacitors and for 10.7 M Hz (FM if transformers) use 30 to 39 pF mica or ceramic capacitors.

First draw a diagram of how the transformer is mounted in the set and label or number the connecting wires and components. Next remove the if transformer from the chassis and carefully pry open the metal housing. With the felt tip marker draw a vertical line across the plastic or bakelite base to help in reassembly. Mount the transformer in the bench vise with the vise jaws holding the plastic or bakelite base securely, but not too tight. With your hand drill, carefully drill away at the central rivet, which is usually hollow for slug tuning alignment. After you have drilled about half way through the rivet, use your small jaw wire cutters to bend the rivet perimeter inward to facilitate removal. In some transformers you may have to unsolder the coil wires from the lugs before removing the rivet. Again, draw a diagram and mark the wires with the felt tip marker. Once you have the transformer apart a small mica wafer will fall out from between the base plates. This piece of mica is coated with metallic silver and there you will usually see the culprit. You see, this silver tarnishes just like your nice silverware, and that brown/black border around the edges of the mica wafer is silver sulfide and acts as a semiconductor. This provides a path for electrons to flow across the mica insulator. With your wire cutters, trim back the metal contacts that used to contact the silvered layers on the mica wafer. This is done to prevent them from shorting against each other after reassembly. Now solder your new capacitors in place and the transformer wires too if they were removed. Often the replacement capacitors can be mounted so that they will fit inside the metal housing. Otherwise, it will be necessary to mount them outside the transformer beneath the chassis. Check the transformer with an Ohmmeter before reassembly. Press the base back together and carefully flare the central rivet back into place . A small solder bead will help to reinforce the abraded surfaces that resulted from the drilling. Be careful not to overheat and melt the plastic base when you do this. Mount the transformer back on the chassis and reconnect the wiring according to your earlier diagram.

You will have to realign the set according to the schematic. In selecting capacitors for FM if transformers, I have found 33 pF mica capacitors to be the best. Use capacitors that are rated at 500 Volts or higher if you are dealing with a transformer power supply sets and 300 Volts or higher for AC/DC sets.

Thank you HVRA member Fred Wuensche for your input and guidance. As I recall, it was you who coined the term "transformer black plague" in the first place and educated me about this pervasive problem.

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