How to Replace Power Transformers in Antique Radios
The power transformer in your antique radio has an input of 120 volts AC, but has several outputs, and not all radios are the same. One output provides 6.3 volts AC to the filaments of the tubes, one or more outputs go to a rectifier to change the output to DC, for bias, control and tube plate voltages known as B+. These voltages can reach up to 300 volts or more. You will need a schematic for your radio and your new transformer, and you must know how to read them.
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Things You'll Need
- Basic electronics technician's hand tools, including soldering equipment
- Pencil and sketch pad
- Schematic diagram for your radio
- Various electronic assembly hardware, depending on the particular radio
- New transformer with a diagram of its specifications
Instructions
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Tubes have a more natural sound. Read the schematic diagram of your radio to find out all the voltages you need on the output of your transformer. Remember to check for filament voltage, bias voltages and B+. To replace the transformer, you must find one with the same number and level of outputs. You must have a suitable replacement to proceed.
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It might work with a new power transformer. Disassemble your radio to the point that you can see the transformer, its wiring and its mounting hardware. Many old radios were considered furniture, and the design was for beauty not function. It may be difficult to find some of the attachment devices, but be patient and determined. Also be careful not to damage it.
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Some antiques have short wave. Remove the wiring from your old transformer at the connection points. Do not simply cut them off and discard them. Following their routing to the connection points will help you install the new transformer. Some connections may be soldered or have screw terminals. Make notes of what wires you remove from what points. Make a sketch. Take note of all wire colors, as that may help you find where to make the new connections.
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Remove the old transformer from the radio. Be careful not to damage old parts that may have become brittle. Be careful not to break any screws or mounting brackets that may have rusted. Try to clean away rust and dirt as your go.
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Install the new transformer in place. You may have to fashion new mounting brackets, as you may not be able to find a replacement with the exact same dimensions or mounting hardware. But if the output voltages match the old transformer, you should be OK. But do not attempt to wire it unless it is firmly in place.
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Connect the primary of the new transformer to the power input of your radio. Check for fuses that may be in the circuit. Use your schematics and your notes that you made while removing the old one to help you find the correct connection points. Try to use the same type of connections as the old transformer, or fashion new ones as necessary.
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Wire the secondary windings of the transformer to the appropriate points for filament voltage, bias and/or control voltage(s) and B+. Use your new transformer schematic, your radio schematic and your notes to help you find the connection points. Solder or use terminal lugs as appropriate.
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Reassemble your radio at your convenience, as you may have other parts to replace or repair. Or you may wish to restore the cabinet.
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Tips & Warnings
If you are working on a radio made outside of the U.S., it may have an input of 240 volts. For use in the U.S., find a replacement transformer with a 120 volt input but the same output voltages.
To find a schematic for your radio, see References. Doug Criner's site lists one free possible source and three who charge a fee.
References
Resources
- Photo Credit vintage radio and gramophone image by jovica antoski from Fotolia.com old radio image by Goran Bogicevic from Fotolia.com retro radio image by Elke Dennis from Fotolia.com vieux poste radio image by Jacques PALUT from Fotolia.com
