The radio restorer's workshop

This article discusses the proper set-up and equipment for an amateur antique radio restorer's workshop. Only facilities for electronic restoration are covered. Apart from these, a restorer may need tools and facilities for cabinet restoration. If you already have a workbench, and I happen to rate some of your gear as rather non-essential, don’t be upset; what you have, you have, and you may need it someday. What I’m trying to do here is help you make priorities for the gear you DON’T have.

I will try to put tools and equipment into the following categories:

So, let’s start building a workbench:

You will need table to work at. It must be stable, with a surface that is durable enough to resist scratches from an exposed radio chassis, drops of solder, the occasional hot component, etc., and reasonably cleanable too. Or, as an alternative, the surface must be easily replaceable, for that, a piece of sturdy cardboard will do. Worktable: Essential.

You will need a good chair to sit on; a swivel chair with adjustable height. Good chair: Essential.

You will need good lighting, both an overhead flood-light and an adjustable lamp. Good light: Essential.

You will need a sufficient number of power outlets readily at hand. The fancy solution is an array of individually fused outlets with switches, but a distributor panel really works equally well. Unless you have a lot of gear that draws a lot of power, you should draw all power from a single wall-outlet; this has some advantages: You can switch everything off at one switch, this is both a convenience and a safety feature. Also, you are sure that all your equipment runs on the same phase; exposed electronics running on different power phases can give you some interesting surprises. Power: Essential.

Finally, you will need storage space for tools, spare-parts, and books, preferably as drawers and shelves under and besides your desk (shelves OVER the desk may look handy, but you risk dropping objects on the radio you are restoring, or getting shocks or burns when leaning over it). Storage space: Essential.

That was the furniture, now for the equipment. Before deciding for equipment, you must realize that even the best equipment is worthless if you don’t know how to use it. For example, as a trained electronic engineer, if I were to choose one and only one instrument, I would pick an oscilloscope. However, it requires both experience and training to use an oscilloscope efficiently, so if your skill level fits a multi-meter better, that would be your essential choice. But let’s try and evaluate various gear:

Before you can repair a radio, you need to be able to take it apart, so you will need an assortment of screwdrivers, from thin pin types for knob fastening screws, to big ones for chassis screws. As you will be working with electrics, they should have insulated handles. Choose medium quality. Cheap and easy to get, there is no need to purchase a large array from the start; a few will do, and then you can supplement your collection as need arises.

Wire cutting pliers. A good pair of wire cutting pliers is not cheap, but worth the price. However they are too delicate for the rougher chores, so you should also have a pair of piano wire cutters for heavy duty. Wire cutting pliers: Essential. Expensive wire cutting pliers: Useful.

A pair of flat pliers and various tweezers: Essential.

Magnifying glass. Some lettering and other things on components may be hard to see, especially if you (like me) are not a teenager. Magnifying glass: Useful

Mirror. A small mirror on a handle, like a dentist's mirror will help you see those markings, screws, and other things hiding in dark corners of your radio. If you do TV sets, a large mirror to enable you to watch the screen while working from behind the set may be essential, and the dentist's mirror is surely very useful.

A word of warning on tools: Stay away from the various multifunction tools that hardware stores try to sell you. If a tool is made to perform three functions, the performance for each will be less than 1/3. The Swiss Army Knife concept is great when you need to carry only one compact piece of gear, but it has no mission on a workbench.

Very importantly, you must have a soldering iron. Don’t save on this; cheap soldering irons perform poorly and wear out quick. Let’s look at the different types:


Now for instruments

Multi meter: You will need to measure voltages, resistances, and maybe currents. A big old analog multi meter looks great on your workbench, but a small, modern, bright plastic, 15$ digital meter will do the job at least as well, probably better. For tuning, however, analog instruments are much better. Multi meter: Essential. Analog multi meter: Useful.

Oscilloscope: As I have mentioned, I personally find the oscilloscope to be a must have, but to be perfectly honest, it is something you could live without. A good new oscilloscope is frightfully expensive; a cheap new oscilloscope is not very good. The logical choice of the radio restorer is a good second-hand scope. Dual-beam is preferable, and if you ever do TV repairs, a delayed trigger function is a real boon. Remember to buy probes; good oscilloscope probes are surprisingly expensive, but worth their cost. Oscilloscope: Useful.

RF signal generator: If you are going to do line-up of receivers, you will need one, but many restorers never do a line-up. RF signal generator: Nice to have.

AF signal generator: Essential for anybody who constructs AF equipment, but not important for the restorer. The tone range of your old radios is what it is; there is little you can do about it anyway. For fault-finding a simple signal tracer is really much better. AF signal generator: Fancy.

Sweep signal generator: A wonderful tool for lining up receivers, provided you also have an oscilloscope, and provided you have the skills to line up a receiver. But it is not an easy task and if you don’t know what you are doing, you may do more harm than good. Sweep signal Generator: Fancy.

Tube tester: Now, this is a hard one, because a certain amount of religion is involved here! Some people routinely check tubes, but "real engineers" are generally skeptical about this practice. A tube that tests in the red for, say, emission or gain, may work perfectly well in a given radio, and a tube that tests out OK can sometimes refuse to work in real life.

And it gets worse: Suppose some fault in a radio makes a tube draw too much current; maybe this fault was there for a long time, and now it has worn out the tube. So, you test the tubes and find this tube to be bad and put in a new (or newer) one, but the real fault is still there and will cause the next tube to wear out prematurely.

On the other hand, if you have loads of old tubes in unknown condition, tube testers are handy for sorting them out. In my opinion, however, a tube tester rates as: Fancy.

Isolation transformer: Again, a certain amount of religion prevails; many old radios do not have a mains transformer, so operating them with an open cabinet is inherently hazardous. However, an isolation transformer only removes some of those hazards, and may lead to carelessness. Constant use of safe handling procedures are the only insurance against electric chock, and the use of an isolation transformer won’t fundamentally change that. Isolation transformer: Nice to have.

Variable transformer or serial bulb arrangement: Just plugging in an old radio in unknown condition is not such a good idea. You may blow otherwise good parts like rectifiers and power transformers, defective parts may blow up, and there may even be fire. So you must have some method for making a soft start, that is, for raising the supply voltage slowly while you watch closely for adverse effects. The best solution, technically, is a variable transformer, but you can come a long way by putting light bulbs in series with the radio under test. The best set up is to mount three or four sockets in a box, wire them in parallel, and put the whole thing in series with the radio (make a short extender cord, open one wire, and connect the ends to each side of the bulb array). Now you can put various combinations of bulbs in the sockets and thus raise the current fed to the radio in several steps. An elegant addition is if you add a switch for each socket, so you won’t have to handle hot bulbs. Some soft start arrangement: Essential. Note: A modern light dimmer WON’T do the job; it works on a different principle!

Signal tracer: A small, battery powered square-wave generator will go a long way for fault-finding. You use it for injecting a signal to a stage to see if the signal gets to the output; if not, there is a fault between the stage in question and the output. As the square-wave is rich in overtones, it also works in IF amplifiers. Signal tracer: Essential. Obviously, if you own more sophisticated signal generators (AF and RF generators, see above), you can do without the signal tracer, but it will still be convenient to have.

Loudspeaker: A loudspeaker in some cabinet for temporary use while testing is convenient. This enables you to test out the rest of the radio, even if the speaker is defective. Many cases of distortion are caused by a defective speaker; they are easily found out by hooking up a known good speaker. Extra speaker: Useful.

LCR meter/capacitance tester: This piece of equipment can check out capacitors, and often also coils. Right away, that sounds like a jolly good idea, but you don’t really need it that often. Coils rarely change inductance (they mostly just become open), and defective capacitors are often easily spotted by other means. LCR meter: Nice to have.

Hans Egebo