Radio Restoration Tips

Here are some tips on restoring old radios that I've picked up that may help you if you are starting off in this hobby.

The most common problems with old radios are:

wax paper capacitors getting leaky due to age. The devices have a limited life. Symptoms are a radio that works poorly or not at all. They can be easily replaced. Either order them from a local electronics distributor or save time and trouble and get them from justradios.com.
electrolytic capacitors failing. These often dry out if the radio is not used for some time. Symptom will be a loud hum. These can also be replaced with modern capacitors which are typically smaller and of better quality.
dial lamps often burn out. Operating a transformerless radio with burnt out dial lamps can overheat and damage a tube, so it is best to replace the lamps as soon as possible.
and of course, tubes can fail, often due to physical damage.

In a transformerless radio, the tube filaments are in series. If one tube has a burned out filament or is missing, none of the others will light up. Like the old Christmas tree bulbs wired in series, you can determine the faulty tube by testing each one with an ohmmeter, or replacing them with a known good tube of the same type.

You can repair rips in speaker cones using paper and glue. One person recommends using brown paper bags and white glue. There are people who can professionally recone speakers, but for a cheap $10 radio it is not worth the cost.

People used to solid state equipment may not realize the potential danger of working on vacuum tube circuitry. Voltages in excess of 300 volts are common and many transformerless radios have chassis that are live or have significant AC voltage present on them. Work on unenergized equipment whenever possible and discharge power supply filter capacitors that can store a voltage when the unit is unplugged. Particularly when working on transformerless radios, use an isolation transformer to reduce the risk of electric shock to ground. Also follow the rule of only using one hand at a time when working on live circuits.

A variac (or autotransformer) is useful for letting you power up an unknown radio slowly until you can determine it has no major problems that could cause excessive current draw and damage components.

Schematic diagrams are available for many old radios. A good source is justradios.com. You can also purchase CD-ROMs of radio schematics, which is cheaper in the long run if you collect many radios. A schematic is not essential though, as many radios use essentially the same design.

The usenet newsgroups rec.antiques.radio+phono and rec.audio.tubes can be a good resource for getting answers to questions from experts.

Thanks to eBay, anyone can now have their pick of hundreds of vintage radios for auction. The down side is that prices on eBay tend to be high and shipping can be expensive and risky for tube radios. Garage sales, flea markets, and garbage day can be other good sources of cheap radios and parts.

There are hundreds of web sites with useful information about vintage radios, test equipment, electronics, and the history of old radio. A google search is all it takes to get started.