So you found one of those old tube radios in Granny’s attic and are thinking of restoring it. Maybe you were at a local flea market and couldn’t pass up a nice looking old tombstone radio for such a low price. Before you take it home and plug it in you need read this first. Knowing these tips may save not only the radio but maybe some body parts.
Tube radios were a part of our electronic history for quite a long time. Most are not as rare as one would think but much time has passed since they were essentially replaced by solid state units. You might plug one in and it seems to work fine. The other side of the coin is things may not go so well.
Essential Skills Required
The necessary skills required for restoring a tube radio vary. If the unit is intact and in seemingly good condition a lesser skill set is needed than if the device is in total disarray.
Tubes generally require higher voltages than modern devices and can be very dangerous. Knowing what precautions to take while working with these voltage levels are definitely prerequisites before even considering plugging in one of these radios.
Danger, Danger, Will Robinson
Aside from the potential for electrical shock, the old electrolytic capacitors could pose a danger. The electrolyte contained in the capacitor can dry out over time and if suddenly charged with electrical current they can explode like a miniature bomb.
Wires can corrode or come dislodged due to deteriorated solder joints. This can create the possibility for human contact that can do more than make your hair stand up. These old units were designed before proper grounding techniques were developed and if you are in contact with the neutral connected chassis you could be exposing yourself to great danger of electrocution.
Powering up the Radio
Once it is determined the unit is in reasonably, good physical condition, and you understand the electronic fundamentals then it is time to plug it in and give it a go. Not so fast, you will need a piece of equipment that is essential to the tube radio restoration hobby.
Buy a 110 Volt AC variable transformer, commonly called a Variac. This device allows you to plug in the radio and bring the radio very slowly up in voltage. You can buy one online for usually around $100. There is a slight possibility the electrolytic capacitors can be slowly conditioned back to service.
The variable transformer will cause the caps to open at lower voltages if they are bad and provide a way to do it without having your hand on the power cable. You may get lucky and bring both units to full voltage without incident. Usually the electrolytic caps will have to be replaced with new ones.
There is much more to it
This article is just the beginning of the journey to restoring old tube radios. Now that you know the dangers and what can be done initially, many other factors come into play.
There are several schools of thought on what is considered a proper restoration. Some believe the integrity of the original components must be maintained. Others think it is alright to replace every, out of spec, component with a modern equivalent. I will be covering this, and more in future articles.
Get ready to spend a lot more money
You are going to need more test equipment, a schematic diagram, and a good soldering station if you are seriously considering restoring these puppies as a hobby.
A professional grade tube tester is a must. Get one that was manufactured later than the age of what you are testing. The older tube testers are useless if they were made before the tube types were invented.
A digital and analog multimeter are basic test instruments on every electronic bench. An audio signal generator and an oscilloscope come in very handy to be able to see what is happening. Schematics will show what waveforms must be present for proper operation and where those stray wires go.
Conclusion
By now, you should be aware of the dangers that are presented when restoring tube radios as a hobby. The main essential piece of equipment you will need is your brain. Fill it with electronic knowledge, buy the proper equipment and you will find that restoring these fine pieces of art a most pleasurable task and rewarding hobby.
Other Related Yahoo! Voices articles by Dave Bolick:
7 Top Electronic Sites for the Hobbyist
Hard to Find Surplus Electronic Pars & Components
Test Instruments Used by Electronic Technicians – Multimeters and Beyond
