03-02-2009, 09:24 AM
Zenith transformers have a tendency to run hotter than most. I believe it was due to the fact that Zenith used the least amount of iron to get the job done. What adds to the problem is the higher line voltages in use today. Many times line voltages today can be as high as 125 to 127 volts. These sets were designed to run at about 115 to 117 volts. What most of us do is install a buck/boost transformer or a power resistor to reduce the line voltage to about 110 to 115 volts. The transformer will run much cooler at these values. There is no sense in stressing a 70 year old transformer.
If you decide to use a power resistor in series with the transformer primary, usually a 15 to 20 ohm resistor of about 20/25 watt rating will be sufficient. It would be necessary to mount it away from other components, since it will run warm to hot.
A buck/boost transformer is a more elegant approach. Usually a 12 volt 1 or 2 amp filament transformer will suffice. It should be wired to buck the supply voltage to the primary of the power transformer. Most likely, a quick search of the radio forums will produce a typical wiring diagram.
Regards,
Ed
If you decide to use a power resistor in series with the transformer primary, usually a 15 to 20 ohm resistor of about 20/25 watt rating will be sufficient. It would be necessary to mount it away from other components, since it will run warm to hot.
A buck/boost transformer is a more elegant approach. Usually a 12 volt 1 or 2 amp filament transformer will suffice. It should be wired to buck the supply voltage to the primary of the power transformer. Most likely, a quick search of the radio forums will produce a typical wiring diagram.
Regards,
Ed
