Whether you are selling or buying a really old radio (those with tubes) it is important to know what NOT to do with them.

The first thing is to NEVER just rush to an electric outlet and try it. After sitting for decades major components - the capacitors (condensers) and wire may have dried out, rotted, or otherwise become hostile residents inside that old circuit.

NEVER plug in an old Zenith without checking carefully. Models made before and just after WW2 used latex (rubber) insulation on the wires and it usually crumbles and falls off as it ages, making shorts likely. Other brands (including RCA around WW2) used the same type of wire. When in doubt, don't even try it before looking under the chassis. If you see yellow or colored particles falling out of the radio there's a good chance it used this bad wire and is unsafe to try without replacing or sleeving the wires..

Also watch out for radios made before 1940. If it has a fat or funny electrical cord do not replace it with a regular cord! It is probably a special resistor cord. Using a regular cord will probably burn out one or more tubes and possibly damage other parts. If the cord needs to be replaced you will either have to find a replacement or make some modification to the radio before turning it on. (See the end of the guide for places to ask for help.)

The greatest usual danger to the radio, and possibly the tester, are the large value electrolytics in the power supply. These can short with years of inactivity and can fry the transformer of some sets and burn out tubes in most. They can also catch fire or even explode in some cases.

Some tube types are also notorious for causing damage when they go bad. The 6X5 (also 6X5G & 6X5GT) is one. Commonly found in old Zeniths and others from 1939 onward, it can short and burn out the power transformer. It should be tested or precautions taken before trying the set. Some collectors prefer to wire around it and use modern solid state parts instead or at least add a fuse to the transformer secondary.

SO, how can you (or someone else) try one safely? If you intend to sell it don't even try. Your bidders will prefer to fix it and test it themselves. But if you are trying it for yourself there are ways to do it, although if you intend to fix it you really should open it up and test or replace obviously dangerous old parts and install a fuse in the power supply to prevent damage. (See end of this guide for where to get parts and advice.)

The quickest and most primative, after at least making sure the wire is OK, is to make a test extension cord. It may alert you to the worst cases but is not foolproof. Also keep in mind that the radio may already have been damaged by either an old failure or by someone else "trying it out."

To make a test cord take a regular extension cord (a Dollar Store one will do) and cut one wire (the one going to the smaller pin if you can identify it) at a convenient placr and splice in a light bulb socket (the kind you see on construction sites that attaches by wires is available at a good hardware store) and be sure to tape up the wires so there's no shock hazard. If you are handy you can also convert a lamp by adding a socket to one wire in a similar manner. Use a 100 watt (regular) bulb in the socket for average table sets. The bulb is now in series with the radio and the voltage across it will be determined by how high the load provided by the radio is. If the bulb glows dim the load is low, bright indicates too much current.

Note: Be very careful with very old radios from before WW2. Not all of these were 110 volt designs. Some were sold for the farm market before rural electrification and ran on 32-volt DC battery systems charged by windmills. These "farm sets" often used the same cords and plugs that were used for regular light circuits or may be missing plugs. Look the set over for signs that it may be one of these, especially if you found it out in the country. If the voltage is not obvious the tube diagram may have a "vibrator", "vib", or item marked "v" on it. This indicates such a set. Never plug it into any AC source. It needs a special power supply or heavy modification to work again. Major makers were Philco, Zenith, Sears (aka Silvertone), and Montgomery Ward (aka Airline).

If it is an AC or AC/DC set proceed.

Plug the radio into the tester cord and watch the bulb as you turn it on. If the bulb glows dim you are OK to test. If it lights up bright or becomes bright turn the radio OFF at ONCE! It probably needs work before it can be tested further or used. When in doubt, turn it off.

Shops and experienced repair persons will use an ammeter (amperage meter) to evaluate a radio at first. They may combine this with bringing the voltage up slowly via a "variac" (variable-voltage transformer), fuses, and an isolation transformer. This protects vital (and hard to replace or find ($$$$) parts.

Depending upon the design it can take 1 second (some portables) 10 seconds (sets with a transformer supply) or up to a minute (series circuit sets) to "warm up" and start making "noise." Listen for any crackling or frying sounds from within or smells of something hot or burning and turn it off instantly if you detect either.

If it does start working do not be surprised if it hums loudly. This is those pesky electrolytics failing in another way. If it does not hum but does not pick up a station or crackle as you turn the volume knob it may have any problem from a simple bad connection or tube (probably why it was put away) to a failure of some internal part, possibly simple/major. Not coming on at all (tubes not lighting) may be anything from a bad tube, cord, or switch to a bad transformer or power resistor. There are many different designs and different ways for them to fail.

Repairs to these old sets can be easy or extremely difficult, depending upon design. In general, simple AC/DC table sets are easy to fix and parts are generally available from collector suppliers or right on eBay. Old paper capacitors will have to be replaced or you risk a failure and possible damage to other parts and maybe even a fire hazard. Again, these parts are readily available in newer and longer-lasting modern versions on eBay or from suppliers. Electrolytics (usually filters) will probably have to be replaced too. Direct replacements are probably not to be found but modern units can be wired in and hidden under the chassis or otherwise used as they are far smaller than the old ones.

Consoles and other more complex sets may require some special knowledge, have greater failures, or require special tools and knowledge to set up. Consult other collectors for help. They can be found on Yahoo Groups, on old radio websites, and on the UseNet newsgroup rec.antiques.radio+phono (check with your ISP for newsgroup availability or use Google groups.)