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Post by Mpaoletta on Wed Dec 25, 2019 12:32 pm

Hello, new here. Was recently gifted my father's antique Zenith. He never knew anything about it, just used it as a decorative piece of furniture. I finally got around to clearing the inside of the cabinet enough to find the model number and take some pictures. I'm hoping to restore it to working condition but don't even know where to begin. Please help..

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Post by Bill Cahill on Wed Dec 25, 2019 4:46 pm

Welcome to TRF. Nice radio.

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Post by Chas on Thu Dec 26, 2019 12:22 pm

Welcome!

The Zenith 73 is part of a series of Zenith radios built around 1929.

Most of the chassis are near identical with variation in the coupling and number of tab in the Automatic tuner.

After 90 years there will be a lot to do but here is a "list" of major faults that can delay restoration.

The automatic tuner has a lighted dial legend with a window of white frosted cellulose acetate. The openings are intended for one to pencil-in their favorite station call letters. The knurled knobs are the threaded locks for resetting the cams that find the stations. Loosen with fingers and hold the tuner drum on the desired station and depress the loosened lever. The cams will reposition and will hold the position when the knurled knob is re-tightened. The lubricant will be stiff after all these years. There is a gum rubber hose over a steel rod that is a bumper for the tuning levers if they are suddenly released. The gum tubing will be hard, it can be replaced with rubber hose from hardware store.

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The main tuning condenser has cast "pot" metal stator brackets and cast mounts for the rotor plates. Some blends of pot metal will degrade from inter-granular corrosion. That will shift the plates of the stators and increase spacing so the condenser will jam and short. The cure is another Zenith tuning condenser OR parts from one to make two. Not all sections of the cap will fail and there are five sections one is unique as its stator rotates. Zenith also tunes the plate circuits of the RF amplifiers. That means for two stators, they are alive with 180 or so volts.

Some restores have found that shorting plates cause the coils in the RF late circuits to go open. The short is not the problem but swelling of the RF coils and breaking the fine wire.

The main voltage divider resistor can go open in one or more sections...

All of the wax paper capacitors in metal can caps will leak badly. "re-stuff" them if need be but creative replacement of the cap with a axial metalized seems to work just fine.

If one or more of the solenoid RF coils are open, usually the open is next to the solder tab a splice repair will fix. If not re-wind same turns/direction/wire type & size

One or more of the audio transformers can go open, a replacement from another chassis will work O.K.

Looks like you will need a compliment of tubes. Do not pay a premium for globe tubes, the ST type are fine and are overall better.

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There are no hard to find tubes. The 45's any that have a low to fair test will work as the radio does not drive them very hard.

The Carpincho leather speaker surround will be dry rotted. Any good chamois will work and careful use of adhesive will fix the speaker. If you find the cone of the speaker brittle it is best to replace it. The 45's can rattle a brittle speaker and cause it to crumble.

The radio does not have AVC so tuning a station can cause blasting of the sound...

I do suggest replacement of all the carbon resistors. I have found they drift under load and will cause fading. Use a carbon film 2 watt, values are 20%. Two watt is larger like the older resistors. Exception is the voltage divider 10 watt is sufficient if you cannot find a whole Zenith divider resistor. The volume control may get noisy, some screen current flows in this control so it has to be in good condition.

The finish on the radio is shellac, soluble in alcohol, be careful with solvents. Clean the cabinet with mild mix of Murphy's oil soap on a damp cloth and do not let the surface stay wet. work the cloth into the carvings. Once the radio is free of dirt, follow up with a damp cloth with odorless mineral spirits, that will remove and old wax residue. Clean until the rag comes away clean. Allow the cabinet to dry several days.

This radio has fine tone but must have a short, direct to earth ground and at least a 50' antenna. Like all AM radios, electrical noise in the home is a problem.

Yes, I have "rigged" my model 53 to use a loop antenna. Very possible to use a Terk or Tecsun loop if it is a long way to earth ground and or the wire antenna is impractical.

YMMV

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Post by Mpaoletta on Thu Dec 26, 2019 7:01 pm

Thanks Chas,
Seeing as I have never worked on any electronic devices previously, let alone one involving tubes, I have decided to seek professional help. Hopefully this project will be underway soon. I'd love to hear it working after all these years

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