I’ve been happily restoring old radios for over twenty years now, and acquired a bit of knowledge along the way. Just as with any antique, there are certain things to be aware of before, during, and after the process of restoration.
What follows here is not so much a comprehensive restoration guide, but more a general list of steps one might take in order to bring a classic vacuum-tube based radio receiver back to life. Most, if not all, of these steps should encourage further research before actually beginning the restoration. These notes also assume the reader has at least a general knowledge of electronics.
Tools: Along with the usual screwdrivers, wire clippers, pliers (regular and needle nose), you’ll need some extra tools: rosin-core solder, a good soldering iron of at least 25 watts, and a multimeter capable of measuring volts, ohms, and milliamperes. I also recommend a pair of safety glasses.
WARNING: Tube-based radios usually contain voltages on the order of 150 – 250 volts in parts of the circuitry. The restorer should take all reasonable precautions when working with such circuitry. Safety first!
- Resist the temptation and do not plug the radio in, “just to try it out”. There are components inside the chassis that, if defective, can cause massive damage. In extreme cases, a restorable radio can be reduced in minutes to a parts chassis. At the very least, the power cord may have unseen nicks or cuts which could lead to a shocking surprise.
- Obtain a schematic wiring diagram for your radio. You’ll need two pieces of information to do this – the manufacturer of your radio, and the model number. The former is usually obvious, and the latter can usually be found on the rear apron of the chassis, or on a label affixed to the inside of the cabinet.
Once you have this information, schematics can be found on many web sites. Nostalgia Air (www.nostalgiaair.org) is a popular schematic site and will probably have what you need, available for downloading. If not, schematics can be ordered from Antique Electronic Supply in Tempe, Arizona (www.tubesandmore.com). If the model number is lost or missing, then giving the supplier your radio’s manufacturer, tube lineup, operating controls (volume, tuning, etc.) and frequency coverage (bands) will usually enable them to determine what model you have.
- Begin the restoration work by carefully removing the chassis from the cabinet. Save all screws, knobs, and other small parts in resealable plastic bags, and label each bag so you know where the parts came from. You won’t remember where they go after a day or two, so let’s keep everything organized from the start. Set the cabinet aside. That’s a separate restoration task and is outside the scope of this guide.
- Remove the tubes and set them safely aside (your schematic diagram will show their places, so it’s not necessary to note this). Carefully clean the years of dust and grime and muck and bugs from the chassis and exposed components. I use a vacuum cleaner and soft paintbrush to remove the loose dust, and then come back with paper towels and a cleaner such as Formula 409. Do NOT use such cleaners on dials, markings, or any other nomenclature, as the cleaner will probably wipe them away. If the chassis is heavily rusted, I sometimes use a rust remover solution to clean it, but take care with such products and use them sparingly. Be sure to remove all traces of cleaner from the chassis when finished.
- Carefully turn the chassis over and examine the wiring. Replace any wires that have broken insulation, and re-solder any that are coming loose from their contacts. Pay attention to the way the wires are “dressed” or positioned about the chassis. Most every wire is where it is for a reason, and moving them around can lead to difficult-to-trace problems later on.
- In the power supply section, along with the large power transformer and rectifier tube, there will be filters called electrolytic capacitors. They look like small aluminum cans, typically about an inch in diameter and one to two inches in height. Plan on replacing them. They’re probably defective, and if not, they can absolutely be counted on to fail soon. A shorted filter capacitor can ruin components such as expensive power transformers, and an open one will result in a nasty hum from the speaker. You can either bridge the old capacitors with new ones, or cut open the cans, remove the old capacitors, and replace with new units to preserve the appearance. Always use electrolytic capacitors whose specifications are at least equal to or greater than what you’re replacing.
- There are other capacitors to consider, tubular and mica capacitors. Tubular capacitors resemble small wax-coated paper cylinders. You can’t determine their condition by sight, unless they’re obviously burnt or broken. Some restorers leave them and only replace those that later turn out to be bad, as determined by troubleshooting. Others replace all of them as a matter of course. I tend to opt for the latter course and, since new capacitors are relatively cheap, replace all tubulars. The mica capacitors resemble small brown squares or rectangles, and may be left alone as they rarely fail.
- Check the condition of the variable capacitor – this is a large component, usually on the top of the chassis, that resembles a lot of aluminum vanes or plates that intermesh as you turn the tuning control. It should turn freely, with no scraping sounds (which sounds would indicate that some of the stationary and movable plates are touching). Clean it well, and take care not to bend any of the plates. Its bearings may require lubrication; use a good-quality machine oil.
- Now it’s time to check the resistors for value. They should be within twenty percent of their value as published on the schematic diagram, unless they’re specified to be ten- or five-percent tolerance. Replace any resistors that are out of tolerance. One thing to note – today, in specifying resistor value, we use K to denote thousands of ohms (such as a 20K resistor) or M for millions of ohms (such as a 1 Meg. resistor). Some old schematic diagrams, however, used “M” where they actually meant “K”, so don’t replace a 20,000 ohm resistor with a 2 Meg. resistor.
- Next, clean any rotary controls, such as those marked “volume” or “tone”, by shooting a good-quality contact cleaner into them. Rotate them a few times to distribute the cleaner and restore performance. Do the same procedure for switches, but not the band switch – that’s covered in a separate step.
- Return to the tubes. Clean them up with some spray glass cleaner, taking care not to remove any markings on the tubes, as you’ll need to know the type number of each tube. The tubes should be tested; it’s likely they’re all good since tubes tend to last, but it helps to know that your tubes are all working in case further troubleshooting is required. If you don’t own a tube tester, you may be able to find a local radio restorer who does have one. If any tubes are bad, replacements are available from sources such as Antique Electronic Supply, or eBay. Radio manufacturers tended to use popular tube types, making locating replacements easy, and it is a myth that tubes are difficult to find today.
- Shoot some contact cleaner into each tube socket. As you do, insert the tube and remove it a few times. This will clean the socket contacts and ensure a good connection. Replace all the tubes in their proper sockets. If any of the tubes have a metal top cap (some do), those can be cleaned with a bit of fine sandpaper. Be gentle, as top caps can come loose and require a bit of super glue to secure them.
- Examine the dial mechanism. It will need cleaning, and probably lubrication as well. If a cord drives the dial mechanism, that cord may need replacement. Radio supply houses sell the exact type of cord for this purpose – I recommend using it, as ordinary string or cord doesn’t work very well. Your schematic diagram will probably have a stringing diagram that shows how to wind the cord correctly. There may also be pilot lights on or around the dial. These small bulbs should be replaced, and new bulbs can be obtained from your friendly local Radio Shack.
- If the radio is capable of receiving more than one frequency band, locate the band switch (it’ll be the front control marked “band” or “range”). This, too, will require a shot of contact cleaner. The band switch will probably have multiple sections – be sure to spray cleaner on each section, just enough to wet the contacts, and then work the switch through all its positions a few times.
- Now, go back over any component replacements you made and check your work. Make sure you don’t have any cold solder joints – these can be identified by looking at the joint. If the joint is dull, heat it up and flow a tiny bit more solder in it. Cold solder joints can cause trouble that’s nearly impossible to locate.
- Examine the power cord. If it’s the old cloth-covered type, replace it with a new one. Otherwise, check for nicks or cuts and replace the cord if needed. The plug should be in good condition as well.
- Examine the radio’s speaker. If there are any tears in the paper cone, they’ll need to be (carefully) repaired using small strips of paper. Common paper glue and brown paper, such as that used to make grocery bags, works well for this.
- Time for the final check. Are there replaced components that haven’t been resoldered? Are all tubes in their proper sockets, and any top caps connected? Some of the tubes may have shields around them – make sure those shields are properly seated. If the loudspeaker terminates in a plug, is it plugged into the radio? Do all the controls turn freely?
- Assuming everything checks out, it’s now time at last to plug the radio in and try it out. As you turn it on, watch carefully for problems: silence from the speaker, smoke emanating from the chassis, or tubes overheating (you’ll spot this immediately if you see a tube’s plate turning red). Should anything be amiss, turn the radio off immediately. Ensure that nothing’s actually burning, and then let the set cool down for a bit. You can return to it later and determine where the fault or faults lie. Should you need help, the Usenet newsgroup alt.antiques.radio+phono, and the Antique Radios website (www.antiqueradios.com) are excellent resources.
Otherwise, you should now be hearing sound from the speaker, presumably radio broadcasts. If so, congratulate yourself on a job well done, and another classic radio rescued from the scrap heap!
I suggest that the potential radio restorer check out the following web sites and newsgroups for further information and tips before tackling any antique radio restoration project.
Antiqueradios.com (http://www.antiqueradios.com) - The “Forums” section of this website has an excellent question-and-answer section where the restorer can often find answers, or pose problems to the group. The site also has a page of useful links to other antique radio websites.
Nostalgia Air (http://www.nostalgiaair.com) - An excellent source for radio schematics, and also features a question-and-answer section.
Phil’s Old Radios (http://antiqueradio.org/index.html) - Phil knows radios. Lots of tips, restoration histories, radio data, and sources. A great resource for the beginning restorer.
The Usenet newsgroups alt.antiques.radio+phono and sci.electronics are good places to find information and pose questions.
Antique Electronic Supply (http://www.tubesandmore.com) and Radio Daze (http://www.radiodaze.com) can supply tubes and most components required in a typical restoration.