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A Structured Approach to Your Work Area...Tools...And Some Philosophy About What and What Not to Do. by Bill Fizette, W2DGB |
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In the last issue we introduced the subject of working with "the old radios" and established that while you have never done this before, you are interested in getting started. We emphasized the importance of researching your project before you begin to disembowel the patient, and listed some readily available. information sources. Let's continue on.
THE WORK AREASure, you can work on a kitchen table, or even on the floor of your bedroom, but it is darned inconvenient. You actually need a private dedicated work area where you can lay out your project and come and go as your situation dictates. Consider it your very own personal radio laboratory space. I use a discarded kitchen counter with drawers--with the sink hole filled in--located against a basement wall. The height is right for standing, and the three feet of clear bench area that results after my tools and parts and bits and pieces of junk take up the rest of the space is about right. The drawers contain tools and some parts. Overhead is a four-foot fluorescent light fixture as well as a reflector with a 100-watt incandescent bulb. The reason for the dual light source: Often I have to turn off the noisy fluorescent to listen to a radio. I layer the work surface with a piece of corrugated cardboard, bent up in back to save those small parts from disappearing into oblivion, to which I have added clean newspaper. As the latter gets torn and dirty, it is easily layered off and discarded. No space? One correspondent tells me of someone who adapted a closet, and another who converted an unused dumbwaiter. Use your ingenuity. Against the wall I have some shelves for test gear, with the three most commonly used items at eye level directly over the work area. These are the VTVM (vacuum-tube voltmeter), the capacitor checker, and the signal generator. On the shelf and on each side I have mounted polarized 110VAC power outlets...you can never have enough of these. Running along a ceiling joist and down to the work area is a 15-foot piece of wire that serves as a makeshift antenna. OK, we have the work area, but before we go any further, I must emphasize that working with these old radios involves potentially LETHAL voltages and currents, far different in concept than the modern solid-state circuits. By lethal I mean that they can kill you if you do something stupid. The early AC sets from the late 20s and 30s and even the early 40s used hot-field loudspeakers as a part of the filter circuits. This was before the invention of the powerful Alnico magnets used commonly today in PM speakers, which eliminated the need for the heavy and expensive field coil. The input voltage to the filter circuit in the old AC receivers was often 350 volts, high enough to power a small transmitter, and with a working current of anywhere from 50 to 100 mA. DON'T TAKE CHANCES...KILL ALL CIRCUITS BEFORE WORKING ON THEM. To do this, pull the AC plug from the source, and discharge the filter capacitors by shorting them to ground. It wouldn't hurt to have a dehumidifier going if you are in a humid basement area, and a non-conductive rubber mat to stand on. Damp basement floors are notoriously hazardous when working with electricity. Finally, don't work on live circuits if you are tired...pack it in and pick up later when you are fresh. It takes only a fraction of a second to electrocute yourself. Let's take this one step further. Install a GFI (ground fault interrupter) outlet, an excellent and inexpensive safety feature. Connect your other workbench outlets to the "load" side, and all the outlets will be protected.
SOLDERING TOOLSI use a 40-watt iron, a good compromise for tube-circuit components. I also keep a 100-watt iron in the drawer for those heat-sucking ground connections to the chassis. A good radio solder is a must. And don't use soldering paste unless it is absolutely necessary for a badly corroded joint or piece of wire that can't be cleaned, and then only the smallest bit. Believe it...sooner or later (it may take years) the acid will corrode the joint.
HAND TOOLSThe sky is the limit here. You will need wire cutters, various types of pliers, a small socket set, soldering probe, wire stripper, socket nut drivers, small wrenches, and so forth. As time goes on you will accumulate more items until you finally decide that enough is enough. I have discovered that medical forceps are very handy. And don't forget to make up several clip leads. Also, a clip board with paper and pen to take notes as I work along is one of my most used tools...perhaps you can remember where that red wire went that you took off last week before you went out of town, but I gave up trying. I draw sketches and make notes, and I keep all small parts and hardware in a box or small bottle. Remember, what you take apart will have to go back together.
TEST GEARYou should start with three items, a VTVM, a capacitor checker, and a good signal generator or surplus military frequency meter, such as a BC 221 or the US Navy LM, or equivalent. It should have modulation. The common serviceman's signal generator is not accurate enough unless you pair it with a frequency counter.If you are going to work on AC-DC transformerless receivers, an isolation transformer is a good idea for general safety...to avoid accidental electrocution! I picked up an old Heathkit some years ago at a hamfest, although you can make one up out of a couple of old TV transformers or a pair of Radio Shack heavy-duty low-voltage transformers, wired back-to-back. AC-DC radios are notoriously dangerous to work on unless you are very careful and know what you are doing, as it is very easy to have the chassis connected to the hot side of the line. We will discuss this later in more detail. One of your first jobs, by the way, will be to restore the test gear to good working condition. I use a lot of old Heathkit equipment picked up at hamfests, and much of it comes to life with a little simple maintenance. We will go into more detail in the next article. Because one of my interests is working on old short-wave receivers, I keep a continuous-coverage communications receiver on the side of my bench. This enables me to receive the WWV frequency standard signals and receiver oscillator signals in the short-wave bands. I find that a World War II surplus BC 348 is quite convenient...it is not too deep, it is totally shielded, and it has a slow tuning rate with a decent calibration. Another item that you will find convenient is one of the small frequency counters that Radio Shack and other suppliers sell. There are other pieces of test gear that will find their way to your bench in due course, but for now, stick with the three basic items listed above.
PARTSLike information, you can't work without them. What you stock or purchase will depend on what you will be doing. At the very least, you will need a source of good electrolytic and by-pass capacitors and resistors, as these are frequently the baddies in an old radio. And, occasionally, a tube or two. Don't use old electrolytics, even if they are new old stock that have never been used. They frequently won't hold up, and you run the risk of burning out an expensive and perhaps irreplaceable power transformer. New ones of adequate voltage ratings are available (but not at Radio Shack, unfortunately) through Antique Electronic Supply of Tempe, AZ, at hamfests, and of course, at the old radio meets, such as the AWA Annual Convention. Other parts can be salvaged from old TV sets and purchased from mail order houses. I salvage all hardware also.
HOW YOU LOOK AT ITFinally, a bit of philosophy regarding this business of "fixing up" old radios. There are many "collectors" who insist that the end result of a restoration project will be a radio with a gleaming, as-good-as-or-better-than-new finish, and that plays flawlessly. Not just an occasional set, but ALL of them. If you have this thought in mind, you are not alone, but consider this. While that early Zenith is your possession, and you may do with it as you wish, remember that it is considered an "antique," and antique furniture pieces that are essentially complete, and with the original finish, should NOT be refinished for the sake of a few dings and scratches.In the same manner, reworking the electronics of a truly rare radio just to hear it play can also be considered a bit of sacrilege. Aside from the fact that refinished pieces can lose up to 50% of their monetary value, if we rework everything there will be fewer and fewer original pieces left for succeeding generations of collectors to study. My own early interest was the National Company HRO communication receiver, introduced in 1934. I have a very early production run HRO (I am only the 2nd owner) that still has the original parts as well as the original black crackle finish. I have elected to leave it alone, cleaned up, but otherwise original in every respect. Since there are (or at least were) lots of original-design HROs around, I found later production versions of the same design to restore and play with. There are techniques for rebuilding original parts, and this argument seems to be never ending, so my suggestion is that you do a lot of reading to develop your own thoughts. Next time we take a look at and perhaps restore to working condition two important pieces of test gear, a VTVM and a capacitor checker. In the meantime, start developing your knowledge base by reading and more reading. The reference I listed last time by Ed Romney is, I repeat, an excellent beginners' book.
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