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This is another homebrew radio from a pile of commercial and homebrew 20’s radios that I purchased in the fall.
The case is oak and had to be repaired at the back as the hinges had broken out. The finish is original and was cleaned then brightened up with a light coat of toned shellac wiped on.
The construction was quite good and the radio performed well with a speaker after repairs.
The radio had seen very bad storage conditions and required a sraying with hot water and detergent after the variable grid leak and audio transfromers were removed to clean out the mouse effluent.
The taller audio interstage transformer was OK but the 3 to 1 Jefferson Chicago transformer was open. On a more valuable radio I would rewind the coil but on this one I was cheap and lazy. A phone coil was used to replace the original core.
This is the coil from the bell ringer of the old "500" type desk telephones. The actual coil is about 1.25 inches wide. These coils vary a bit but are roughly 2.5 to 3:1. Coil resistance is about 900 ohms primary to 2700 ohms secondary and have proven to be a good replacement for 20’s audio interstage transformers. I would not use them on later AC sets.
To use this coil I dissasembled the Jefferson, saved the steel laminations for a later rebuild and made a wood frame to hold the coil and fill out the transformer case. When the steel band and end shells were replaced the transformer looks original except for the bolts replacing the rivets.
These old phones are getting hard to find now as collectors want them. Rather than destroy a good phone I look in flea markets etc for ones that go cheap due to damage, pizza labels or other marks that destroy their value. Ironically I used to spend a day a week in the factory that made the phones and these coils but did not know their repair value at that time.
Ed.
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