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Archive-name: antiques/radio+phono/faq/part8 See reader questions & answers on this topic! - Help others by sharing your knowledge Rec.antiques.radio+phono Frequently Asked Questions (part 8) Revision Date Notes 1.0 Oct 28, 95 New section Part 8 - Tools and Test Equipment ------------------------------------------------------------------------------ FAQ editor: Hank van Cleef. Email vancleef@netcom.com This is a regular posting of frequently-asked questions (FAQ) about antique radios and phonographs. It is intended to summarize some common questions on old home entertainment devices and provide answers to these questions. [faq editor note Oct.'95. This is a new section, which includes material previously covered in other sections, as well as new material]. This section of the FAQ is divided into two parts: tools, and test equipment. The section on tools is intended to be general, covering tools suitable for working on acoustic phonos and other mechanical devices as well as electronics. The section on test equipment is primarily electronic. TOOLS: If you are going to work on anything yourself, you will need some hand tools. Keep in mind that "tools" and "trades" go hand-in-hand. Most tradespeople are expected to own their own hand tools, and the best sources of good tools are those that sell to crafts trade users. Anyone whose livelihood depends on use of hand tools will tell you that there are two kinds of tools: good tools and no tools. A cheap tool is worse than no tool. It will cost you some money to buy a suitable assortment of proper hand tools for various jobs. Good tools properly used will last a lifetime, and you'll get a good return on the investment. I have tools that I bought over forty years ago that still work "like new." Craftsmen (and women) who use tools professionally will tell you that cheap tools are "knucklebusters" (and worse). There is no substitute for having the right tool for a job. Trying to get by without proper tools for jobs, or with cheap tools, you'll damage the work and hurt yourself. Take the time to learn how to use your tools properly. A quick trip to the library will produce books on various crafts trades that include selection of tools, use of tools, and maintenance of tools (such as cutting tools) that require maintenance. Talk to crafts people in various trades. The automobile mechanic may tell you that Snap-On tools are overpriced and frosting on the cake, but that same mechanic buys every week from the Snap-On truck. And the welder will question whether Linde double-diaphragm gas regulators are really needed, but that's probably what he is using for gas welding. There is an old adage that "the poor workman blames his tools." Develop your skills in using good tools, and you'll get good results. One point of etiquette: If you are talking to a crafts person, don't charge over to his/her toolbox and start looking around. Ask permission before handling someone's tools. Most crafts people will gladly show you what they use, and tell you why they value particular tools. Q. What do you consider basic tools for working on old phonos or radios? A. There are a number of common small tools for working with any small device. These are: a. Flat-bladed screwdrivers. You will need an assortment of these in various sizes. b. "Phillips" cross-point screwdrivers. The also come in various sizes. The most common is #2, but you will also want #1 and #0. The tips on these wear out, and the only solution for this is to buy good quality replacements when the tip becomes worn. c. Hex socket keys, commonly called "Allen Wrenches." Start with a kit that has the common sizes, from .050 through about 1/4 inch. The most common are the "L"-shaped keys. They are also available in screwdriver shanks with straight bits. Once again, these wear out. You can grind the worn tip off one to give it more life, and buy the various sizes individually. Most people working on old electronics have several .050, 1/16", and 5/64" keys as these are the ones most frequently used in small work. d. Socket wrenches. A 1/4 inch drive set in a box, with ratchet, screwdriver handle, and extensions, is a good choice. You can also buy nut drivers, which are screwdriver shanks with socket tips. The "six point" (or hex) sockets are best unless you actually need to work with 12-point hardware. Most commonly used are 1/4", 5/16", 11/32" nut drivers. 3/8", 7/16", and 1/2" are used on binding post, switches, and potentiometers. For these, a ratchet and deep socket is best. e. Box and end wrenches. These come in a variety of styles. A box wrench has a hex shape at either end, two different sizes. An "open end" wrench has fork-shaped tips with parallel sides, also made with tips at both ends, two different sizes. A "combination wrench" has an open end at one end and a box at the other, same size at both ends. Box wrenches are generally made with the box ends offset from the wrench shank. Open end and combination wrenches don't generally have this offset, but the box end of a combination wrench is generally set at a small angle to the shank so that the wrench shank has clearance above the work. Which is best? Most people use all three types in their work. The open end wrench will tend to spring and round off the corners of the hardware if a lot of torque is required, and most people feel that the box ends should be used except where clearance requires use of the open end. Note that there are specialty "tubing wrenches" for use with hex fittings on tubing. These are box sections with a cutout to go over the tubing, to get a good grip on the fitting. These should be used only on tubing fittings, not as general wrenches. f. Pliers. These come in a bewildering variety of sizes, shapes, and tip types. Many people also try to use them instead of wrenches or other more suitable tools, which is not good. Pick pliers for pliers applications, and get the right tools for other hardware tasks. For small work, needle-nose pliers get steady use. You will want to have a set with a very long narrow set of jaws and another that is larger and more blunt, generally called "round nose." Both have long parallel jaws and a rounded tip cross section. A pair of "duck bill" pliers is also quite useful. The common slip-joint "gas pliers" can be useful, but many people consider them a tool that works poorly on a variety of tasks and not very well on any of them. For large work requiring sturdy jaws, a set of "Channellock" (TM) pliers is much better. The originals were made (and patented) by Channellock in Meadville Pa., originally named "Champion Dearment." Get a set that have the interlocking channels for adjustment. g. Diagonal pliers, wire cutters, side cutters, etc. These names are all applied to plier-type tools with cutting tips. You will want a small set for cutting wire. Some of these are made with the cutter tips ground all the way to the very end, which is useful for nipping wire loops on old electronics terminals. They are intended for cutting soft materials, like copper wire, and can be damaged by trying to cut hardened steel with them. h. Hemostats: These look like scissors, but have duck-bill tips on them and a latching mechanism on the handle. Originally used in medical work for clamping off blood vessels. They were used in electronics as "heat sinks" for soldering germanium semiconductors, to bleed the heat off the lead. Also valuable for use in applying clamping pressure to thin sections. i. Magnifying lenses and eye protection. You will want some sort of magnifying glass, jewellers loupe, or bench magnifier, for examining things in detail. A 5X magnifier is a good choice for most work. Always have eye protection when using tools. If you do not wear eyeglasses normally, get some safety glasses. Corrective lenses must be the "shatterproof" eye protection type, and if you wear corrective lens eyeglasses, get a pair that is suitable for close work that has shatterproof lenses. Contact lenses do not provide eye protection---have something in front of them. j. If you are going to do really small work, like meter movements, a set of jeweller's screwdrivers is a good investment. Brookstone sells a kit in a box that includes an assortment of small flat-bladed and cross-point screwdrivers, tweezers, small cutting pliers, and a magnifying glass. Q. Where do I get good tools? A. You can get them from sources that sell primarily to the crafts trades. Most independent automotive jobbers carry automotive tools such as SK and Herbrand. Snap-On tools are sold by independent sales people whose "store front" is usually a step-van type truck (similar to a UPS or bread delivery truck). Other brands are also sold by independent people operating out of delivery trucks. These people make regular rounds of automobile and aircraft repair shops, and are often not listed in the telephone book Yellow Pages. Look under Snap-On, SK, and Herbrand in the white pages. It may be necessary to inquire at an auto repair shop or two, or at an airport fixed base operator maintenance facility, to find out when the various tool dealers normally arrive, and how to get in touch with them. You can generally arrange a mutual meeting point with these people, either on their normal route, or by appointment. Almost all of them know their tool lines and their uses extremely well, and can advise you on what to buy, knowing what uses you plant to make of them. Be prepared to spend money. Most electronic distributors carry good selections of specialty tools for electronics work. The best sources are those to sell to the trades. Don't look for prices, look for quality. Those who sell tools will sell to an individual for the same price as they sell to crafts people in the trades. Keep in mind that good tools are, by and large, not "consumer items" that you'll find in "low price" type stores, such as K-Mart and Wal-Mart. The one exception is Sears, Roebuck, who have historically sold good quality tools under their in-house "Craftsman" name. I have recently heard reports that Sears quality has become less reliable. Also, while Craftsman tools were historically good tools, there are a good many tools that are much more refined, and are worth the extra money in productivity. SK, Herbrand, Blackhawk, Krauteur (pliers in particular), and Channellock are all excellent in the USA. Snap-On is the "Rolls Royce" in automotive type tools, and generally cost more for tools that may or may not be superior to some of the other brands, but you'll find all of these brands in a mechanic's toolbox. Q. What about soldering equipment for electronics work? A. All of the manufacturers that use solder to connect electronic components run "solder school" for new employees. Electronics soldering is not the same as soldering pipes in plumbing or doing auto body lead work. There is only one way to learn, and that is to do it. You will need: a. Soldering iron. A Weller or an Ungar "solder station" with a 35-50 watt "pencil" iron and thermal control in a soldering iron holder is best. If you are going to unsolder components directly soldered to a chassis, you will need at least 50 watts, and maybe a larger 100 watt iron. Do yourself a favor and buy a good soldering station. It will cost more than a cheapie Radio Shack iron, but you will find that the tip stays in good condition a lot longer, and that you do much less damage with heat, using a good iron. The solder station holder provides a place to put the iron down that is safe, a real "plus." Also, buy an iron with a plated iron tip, or get one for it. There is just no way to keep a copper tip well-tinned for this type of work, and solder eats away the copper, ruining the tip after a while. b. Solder. Kester or similar ROSIN CORE solder is sold specifically for electronic use. It is "eutectic" solder, that is, 37 percent lead, 63 percent tin, which melts at the lowest temperature. Don't use 60-40 plumber's solder, which is 60 percent lead. c. Small tools for use when soldering. You will want some fine point needle nose pliers, some medium point needle nose pliers, and a small set of diagonal cutting pliers. Also, a small screwdriver and a solder "pick" that has a pointed piece on one end and a v-notched piece on the other. Round this out with a solder sucker (a little pump with a high-temperature plastic piece that you can safely shove into hot solder, and a button trigger to trip the pump). Solder "wick" works well, but remember that when you are removing solder from a 1934 radio terminal, you are removing 4 or 5 times the amount of solder used on a modern printed circuit board---use the pump to remove most of the solder and the wick to remove the rest. Tin your new iron, and keep the tip well-tinned at all times. This means keeping a coat of unoxidized solder on the tip. The solder stations come with sponges. Wet the sponge, and wipe the hot iron on it to clean off residue. To tin the first time, just melt some solder on the tip. The rosin in rosin core solder is a mild flux---that is, chemically active to deoxidize and clean the surface so that solder will flow onto it. Wipe the iron back and forth on the sponge to distribute the solder. When properly tinned, the tip should be shiny with fresh solder all around back about half an inch. Keep the tip looking like this, and you'll eliminate half the problems people have when soldering. To remove components, heat the old joint until the solder melts, and remove the solder with the solder sucker. Bend the old component leads back, and slide the lead out. You'll have to keep the joint hot until you've got the bent-over part of the old lead away from the terminal. This sounds easier than it is. You will want to learn to use the solder pick, small screwdriver, and needle-nose pliers on various joints. If the component you are removing is scrap, clipping the lead and leaving a short loose end often makes getting the loop open easier, and once the loop is open, the lead can be removed by pushing the wire through the terminal. Also, using the nippers (carefully!) to nip the wire loop so that it will break often helps when removing components. Watch out what you are heating, and watch out what you are pushing and pulling on. That iron is hot and will burn wire insulation, melt polystyrene (clear plastic coil forms), etc. Move things out of the way so you have a clear shot at the joint you are working on. Don't bend terminals back and forth---they'll break. The worst ones for breaking are on the 7 and 9-pin miniature tube sockets, and if you break one, you get to replace the socket, which is a major task. Coil form terminals are not far behind, and most of those old coils are irreplaceable. The big terminals mounted on phenolic terminal strips are fairly rugged, and components fastened to them are a good place to get some experience before tackling finer work. On fragile terminals, once the solder is removed (use solder sucker and solder will to remove as much as possible), a little judicious use of nippers to cut wires, and other little tricks you will learn as you go along, to avoid any stress on the terminal, is the only way to go. Another trick is to make a cold solder joint. Just wiggle the lead a little while the solder cools, and it will stay free. You can then work with two hands to get the joint opened up and the lead out of the hole. When installing new components, run the leads for all new components going to a particular terminal before soldering any. Form the leads into new loops and nip off the excess. Place the iron against the terminal and melt some new solder by pressing it against both the iron and the terminal. It will melt on the iron first, then into the terminal. Don't use too much solder, and make sure that the solder flows onto all the wires and onto the terminal. Once the solder has flowed into the joint, remove the iron and wait for the joint to cool and solidify. This is where cold solder joints occur. A cold solder joint happens when a lead gets wiggled as the joint is cooling, preventing formation of a solid bond. They are generally easy to see, because the solder ball on the terminal will often be very frosty, and not have a smooth surface. They are also very easy to make, and you should experiment with some scrap---just wiggle the pieces as the solder is cooling, and you'll get a cold solder joint. If you've got any doubt about a joint, reheat it and reflow the solder. Cold solder joints are the single most common solder defect. Inspect your work carefully after soldering, and if there is the least doubt about the joint, reheat it. Excess solder and solder bridges (where the solder flows between adjacent terminals) are other quality problems---remove excess solder, and inspect carefully. Many radios were "unrepairable" simply because of bad soldering somewhere. Attention to producing the very best workmanship, and close inspection, will produce quality solder joints----anything less will produce trouble. While the people who originally built these radios were very skilled, you'll occasionally find a cold solder joint or a joint with no solder at all on a lead that has been there as long as the radios has been around. Don't be afraid to inspect, reheat, and reflow a fifty year old solder joint that looks suspicious just because it has been there for fifty years. There are two schools of thought on rosin removal. You can leave the rosin on the joint, and most radios were made that way. However, if you do want to remove it, isopropyl rubbing alcohol on a Q-tip will melt it right off. Q. I need to solder some sheet metal, and my soldering iron won't melt the solder onto the metal. A. The soldering process for electronics work is conceptually the same as for sheet metal, but uses small irons, mild fluxes, and eutectic solder (63/37 or 60/40), which melts from solid to liquid state very quickly. For sheet metal work, there are several processes that are used, depending on the metals to be joined and the strength needed. These can be divided into three categories: a. Soft solder, using pewter (tin-lead alloys). Requires use of a large soldering iron or a flame such as a propane torch. May require strong fluxes and use of 50/50 or 37/63 solder, which has a mushy state and can be worked with paddles or a damp rag. Most radio sheet metal work is done with cadmium plated parts, which will solder with rosin flux. b. Brazing, which is a similar process, but uses copper or silver alloys and a much higher temperature than soft soldering. Requires an oxy-acetylene torch and appropriate fluxes. The principal difference between brazing and soldering is that non-pewter alloys and much higher temperatures are used. Silver brazing is often called "silver soldering." c. Welding, which involves melting the metal of the parts and using a similar alloy as a filler to join the parts together. This requires use of high temperatures to melt the metal. Principal methodologies are oxy-acetylene "gas" welding, traditional electric "arc" welding, and inert gas electric welding, such as "MIG" or "TIG." There are other electrical processes such as resistance, or "spot" welding. I mention all of these because you need to recognize where these processes were used in original manufacture. For radio work, soft soldering on sheet metal parts generally involves lead attachment, and is best done with a 75-100 watt iron, using radio solder and rosin flux. Don't attempt to repair brazed or welded parts with soft solder if any strength is required. While brazing and gas welding are conceptually simple, most hobbyists do not purchase the equipment necessary, and both require some experience to do well, particularly on small work. TEST EQUIPMENT The most frequently asked questions are about tube testers, and many people who are attempting to get their first radio working assume that a tube tester is the first piece of test equipment needed. This is not the case. In a recent discussion between "old-timers" on the boatanchor list who had worked professionally in manufacturing plants during tube days, it developed that none of them recall seeing a tube tester in places like Tektronix, James Millen, or Automatic Radio. While vacuum tube (or valve, to the British speakers) faults are historically the most common faults found in old electronics, most of them can be quickly diagnosed in the application circuit. Also, there are many subtle faults that a tube tester won't find. We'll discuss tube testers further down, but will put discussion of other test equipment first. Q. People talk about using a "Simpson meter." I'm tired of hearing about Simpson. And what do Simpsons have to do with electronics? A. The Simpson model 260, first produced right after WW II, is the most common VOM (volt-ohm-milliameter) found in both manufacturing and service establishments. It is a 20,000 ohms/volt (DC) multimeter, that measures DC and AC voltages, currents, and DC resistance. Simpson is the name of a manufacturer of meter movements, as well as complete multimeter products. The Triplett 630-series is a direct competitor, and some people prefer the 630-NA over the Simpson 260. Both are still produced, and cost around $150-175 for the basic models. A good VOM can be used to diagnose about 99% of the faults in old electronics if you know how to use it effectively. It is the first and most important piece of equipment to have on your bench. You'll rarely see a used VOM for sale, because they are workhorses, and everybody who has one is either using it or has managed to reduce it to junk by using it for decades in all types of conditions. There are inexpensive VOM multimeters for $25-$50 available from places like Radio Shack, if you don't want to pay the price for a good commercial quality meter like the Simpson or Triplett. Either you have a VOM or you need to get one now. Q. What other test equipment is "basic" for working on old radios. A. For most work, the basic instruments that will do almost anything are a VOM multimeter, a signal generator, and an oscilloscope. This has been true since the mid-1950's, when oscilloscopes that were sufficiently versatile for general purpose use became available. There are a variety of signal generators that can be found in the flea markets and hamfests. For radio work, you will need something that produces modulated and unmodulated signals between the IF frequencies and the high end of the receiver bands, as well as a suitable audio signal for testing audio circuits. A generator capable of generating signals from 100 Khz to 110 Mhz, and a fixed 400 Hz audio tone, will cover the needs of AM long wave, medium wave (US AM broadcast) and high frequency (1.6 to 30 Mhz) radios, and cover the 88-108 Mhz. FM band as well. Two items that were very common in service shops in the 1940's, but which are more-or-less forgotten today are the VTVM (vacuum tube voltmeter) and signal analyzer, or signal tracer. We'll look at both below. Used test equipment is generally available at very reasonable prices. Unlike the costs of hand tools and soldering equipment, it is easy to build up a very adequate bench full of useful items for about $100. Q. I saw a Hewlett Packard signal generator at a hamfest, and, at a nearby table, a Hickock signal generator. I know that Hewlett Packard is supposed to build top-notch test equipment, but the Hickock generator was a lot less expensive, is smaller, and seemed to cover almost the same ground as the HP generator. What's the real difference here? A. Essentially, the "real differences" are that Hickock equipment was generally low-price test equipment targeted toward service shops. HP equipment was costly, and generally bought by research and engineering organizations. As you note, the Hickock unit is smaller. Look inside, and you will see home entertainment type construction, with light sheet metal work, inexpensive components, etc. Inside the HP box, you'll find things like huge aluminum castings, top quality components, and more refined circuitry. The products may have performed similar functions, but were designed with entirely different philosophies, and targeted toward entirely different markets. One I would call "service grade," the other, "laboratory grade." Generally laboratory grade instruments were used by highly skilled professionals in laboratory environments. The service grade boxes were often hauled around in the back of a sedan delivery or pickup and pretty well beaten up, and weren't expected to last forever. The reason you see so much laboratory grade equipment in the used market today is that it is thirty or forty years old and lived all its life either in a laboratory environment or in storage in the back of an test equipment pool area. Below are some of the brand names generally associated with the two grades of instrumentation. 1. "Service Grade." RCA (signal generators, oscilloscopes, meters, tube testers). Hickock (signal generators, tube testers). Supreme (signal generators, multimeters, tube testers). Radio City Products (signal generators, multimeters). Eico (a broad line of manufactured and kit instruments). Heathkit (a broad line, kits only). Simpson (multimeters). Triplett (multimeters). 2. "Laboratory Grade." Measurements Corp. (Signal generators, grid dips), Boonton Radio Corp. (Q-meters, other LC instruments). Allen B. Dumont Laboratories. (Oscilloscopes). General Radio (A broad line, including RLC bridges, signal generators). Weston instruments (meters of all types, standard cells). Hewlett-Packard (broad line of test equipment). Tektronix (Oscilloscopes and related equipment). Marconi (British. broad line of test equipment). Philips (Netherlands. broad line of test equipment). Leeds and Northrup (voltage and current calibration). Guildline of Canada (voltage and current calibration). Waterman (oscilloscopes). James Millen (grid dips, frequency standards, specialty oscilloscopes). Wavetek (signal generators). Q. What about VTVM's? I notice that you can get a "service grade" RCA VoltOhmyst or a "laboratory grade" HP or Ballantine unit. Are the HP and Ballantine meters really superior to the VoltOhmyst. A. I have WV97A and WV98C VoltOhmysts, and HP400D AC and 412A DC VTVM's. The meters that get the most use in my work are the WV98C and the HP412A. I like the WV98C because it has both AC and DC capability, and a reasonably good ohmmeter. It is also much more responsive to signal changes, and is much easier to use for a lot of service tasks. The 412A is extremely accurate across the scale, much better than the WV98C, and has a maximum full-scale sensitivity of 100 microvolts, compared to the WV98C's 500 millivolts. It also has a much wider ohms range, and is more accurate there, too. It won't measure AC voltages, and the design cuts off AC response at only a few Hz, so it is slow to respond to changes. In short, the tradeoffs are not only construction quality, but in flexibility. The WV98C required some component replacement when I got it, but it is a much better setup for general service work. The HP meter needed a light bulb replaced in the chopper, but was essentially "plug 'n play" and didn't need recalibration. The HP400D is an "AC meter," and the WV98C has "AC" voltmeter functions. However, the 400D is a true RMS meter, while the WV98C is peak-reading. That is a major difference. If you are looking at the calibrator output of a Tek scope, which is a square wave, the WV98C reads the peak value, and you have to read that value on the "P-P" scale. The 400D reads the equivalent DC energy value of the square wave, information that is not particularly useful if you want to see if the calibrator is anywhere near accurate. RMS measurements have plenty of value when looking at something like a class C amplifier. The 400D was also something of a bear to get working properly, because it had been "fixed" by someone who did not know the principles of operation, and who "repaired" all sorts of things except what was actually wrong with it. In short, all three meters have their place on my bench, and in several applications, one will not substitute for another very well. One point that should not be overlooked is that the sophisticated circuitry of a laboratory grade instrument can be a nightmare to trouble shoot and repair. The WV98C does not have a chopper with lightbulbs, a clock motor, and optical switches, which had problems in the HP412A, and has only a rudimentary power supply, so does not have the regulator problems that were the actual fault found in the HP400D. You can get a great deal of good use out of a service grade VTVM over and above what you can get from a passive VOM. Input impedance is much higher, so you can accurately measure things that the VOM can't see. You can invert the DC sensing and measure negative voltages directly, and the ohmmeter function has a lot more capability than is available with a VOM. While one quickly gets used to the backward-reading ohmmeter scale on a VOM, I still like the VTVM's forward-reading ohmmeter. Q. What about signal tracers/analyzers. You mentioned these. What do they do? A. These came in several configurations. The fanciest ones were the RCA "Rider Chanalyst" and Meissner Chanalyst. Essentially, what they are is a substitute radio receiver, in sections, that you can use to duplicate the functions in a receiver under test. The simpler units had only a crystal video receiver (i.e., an untuned detector and an audio amplifier). The RCA Rider Chanalyst has a built-in signal generator and VTVM. The trouble-shooting methodology for using one of these boxes effectively is to start at the receiver front end, and use the probe to listen for signal. Simply trace forward with the probe until you find where the signal disappears or becomes garbled, and you've found the area that is faulty. Instead of reading meters or scope traces, your ears tell you what's going on. The RCA Rider Chanalyst was in a self-contained box that could be tossed in the back of a car, taken out to a customer's home for a house call to visit a sick Philco Chairside. Probes, power cord, and even the instruction manual clipped inside the front cover. Armed with a tube caddy, a soldering iron, and an assortment of resistors and caps, the set could be brought back to life in short order. Needless to say, the customer could watch all this, be impressed by the "doctor's" widget box and bedside manner---and hear for himself (or herself) the walkthrough that located the trouble. The smaller units, like the Philco, Sprague, and McMurdo Silver units, were not all-in-one boxes, but worked with a signal generator and multimeter alongside. Q. I have a chance to get a Tek 535 oscilloscope with some plugins for a very reasonable price. Is this a good thing to have, particularly when you say that oscilloscopes were rare in service shops in the 30's and 40's? A. Grab the scope, if it is working and calibrated, and has had the selenium rectifiers replaced with silicon (Tek made conversion kits for this). There's been some thought given to coming up with a Tek Scope Faq. Stan Griffiths published a very good little book (available from Antique Electronic Supply) on old Tek scopes named "Oscilloscopes: Selecting and Restoring a Classic." Both Stan and I worked for Tek, and we've been holding something of a steady forum on the boatanchors list on the topic. In the used market, Tek scopes abound, for quite low prices, considering what they are. The most common models are the 545A, 535A, and 547. Almost any of the others in the 530-540 line are good scopes that come back to life quite well and give yeoman service. The common plug-ins for these are the CA, K, and G, and you will want at least one, if not all three. The 547 requires a 1A1 for full bandpass, but will work with any of the letter series. These scopes are big and heavy, around 65 lbs, and gobble up about 500 watts of power. On smaller scopes, the 561A with plug-ins is a good scope, although limited to 10 Mhz bandpass. The 310 is a little (3" tube) cutie that can be very handy, although they are somewhat prone to overheating if you try to run them all day. I'm not going to try to sum up what is in Stan's book here. He has 200 pages devoted to descriptions of old scopes and plug-ins, and the vast majority of the equipment described is good for working with radios. The later 7600 series scopes with the right plug-ins are also good choices, but tend to be more expensive, and more difficult to repair. I'd pick any of these over the 585 (which does NOT work with letter-series plug-ins unless you have a special adapter), some of the specialty scopes like the 517, 519, and 502. On other brands of scopes, Hewlett-Packard tried to compete with Tektronix for a while. Some of their scopes, particularly the lower performance units, were fairly good, and some others were marginal. The Fairchild-Dumont 766H was at least the equal of the Tek 547. However, so far as I know, they are more or less orphans today, with very few people having documentation, spares, parts units, etc. Other scopes? Most of the others are much lower performance scopes than the Tek 530-540, and a good many of them are lower quality as well. Unless you are a scope collector, don't bother with the WWII-era P4 synchroscopes, the old RCA's, or the pre-Fairchild Dumonts. One particular group of scopes to avoid is the Lavoie, Hickock, and Jetronics "Tek wannabe" scopes that government agencies bought in large quantities. These, along with "Tek wannabe" plug-ins, are easy to spot. They look like Tek stuff, but don't have any manufacturer's name on them. Identification is by a screwed-on nameplate. Genuine Tektronix has the Tek logo, the name "Tektronix," and other very clear markings on it. These are, to be blunt, nothing but electronic junk. My personal preference is for simpler scopes. I use a 533A or a 310 for most work, and don't find myself at all hampered by 15 Mhz bandpass (533A) or lack of a delaying sweep (useful for pulse and digital work), or a dual-trace setup. The real value provided by an oscilloscope is in qualitative graphic displays. For serious quantitative measurements, other test equipment is simpler and more accurate, and it takes a good deal of skill and experience to set up and use an oscilloscope to make good quantitative measurements. While you can buy "repairable" Tek scopes and plug-ins regularly for $10-$50, I feel reluctant to advice the novice to run right out and to this. Stan Griffiths has about as much experience working with Tek scopes as anyone, and I certainly would not want to get into a productivity contest with him. Both of us feel that trouble-shooting a sick scope is fairly straightforward and easy, and we buy "repairables" and fix them fairly quickly and easily---most of the time. But a 545 has something like 75 vacuum tubes (I never counted all of them---there are eight here, ten there, seven more another place, etc.), and someone who is not familiar with Tek scopes and trouble-shooting methodologies in general might have a terrible time. Both of us have bought stuff and found, when we started trouble-shooting, that someone had been there before us and "fixed" almost everything except the real problems. It's obvious that somebody else tried to fix some of these, and couldn't. Both of us have specialized test equipment, and both of us know how to set up a completely uncalibrated scope. For someone who isn't really prepared to play "scope wizard," and who wants a solid, reliable scope, finding someone who knows Tek scopes and who has clean-working-calibrated units for sale for $125-$150 may be a lot better bet. Q. Ok, I've read through all the blather about meters, signal generators, and oscilloscopes, and my question was about tube testers. When are you going to talk about them? A. Ok, fair enough. Roughly, tube testers can be divided up into a few categories. (Your FAQ editor is flying somewhat blind here. I don't own or use a tube tester of any type, and it has probably been forty years since I tried to use one. Dan Schoo has kindly furnished material on tube testers, which is included after this general discussion). 1. Emissions testers. These are the type that used to be seen in drug stores, and the Heathkit "Tube Checker" type of box. They are fairly simple, have a heater/filament supply, a "good/?/bad" meter. They generally operate by connecting the tube as a triode and seeing how much current will pass through. Short circuit testing is by applying a voltage across element pairs and seeing if enough current will pass to light a neon bulb. 2. Transconductance testers. The best known of these are the Hickock testers, both the civilian and the military models. As with the emissions testers, they are provided with a heater/filament supply and a shorts test arrangement. However, they are provided with separate DC supplies and controls for setting the tube elements at one or more operating points. Readout, as with the emissions tester, is on a meter which indicates plate current. Most of these have two sets of settings for the meter readout. In one mode, the meter reads the current as DC transconductance. In the other, the meter reads on a "Good/?/Bad" scale. The controls for setting the operating point parameters and meter sensitivity maybe either potentiometers and switches, or sets of contacts operated by a punched card. The type that uses potentiometers and switches is generally used with a tabular listing (a roll chart in the machine) of switch settings and readings. I am not sure how the pots and switches are calibrated, and how easily one can reset the operating point parameters, or read current values on the meter, for taking a series of operating points to plot on a graph. I haven't seen any discussion indicating that anyone is using them other than with the tabular chart values for specific tubes. 3. Tektronix 570 Vacuum Tube Curve Tracer. This is a specialty oscilloscope that can trace out families of operating curves on a CRT X-Y display. The box is provided with a heater/filament supply, two adjustable "fixed" voltages (i.e., they remain static during tracing), a step voltage, and a sweep voltage. The display monitors current (vertical) vs. voltage (horizontal), and may be switched to different suppiies. Connections to the tube are via a patch panel at the front of the unit, which uses jumpers to go to an adapter plate. Two of these are provided, to allow side-by-side comparison of two tubes, and there is a switch to select which set of jumpers is active. While the switches are marked "plate," "screen," "grid," etc., the patch panels allow connection of any of the voltages to any of the elements. This device is not really a "tester," because it has no built-in settable criteria or indications for "pass" or fail. The box can be set up to provide a dynamic display of any set of curves, including such things as suppressor and screen grid transconductance. These were low-volume products, and the 570 was discontinued in the mid-1960's. So far as I know, principal use of them was to match pairs of tubes for various characteristics. Prices on the used market have been bid ought of sight by the golden-ear tube audio crowd, and the last I heard, the going price was well over $1000. All of the above devices are DC tests only. While the Tek 570 provides a dynamic display, it does so at very low audio frequencies. The emissions type tester is clearly a rudimentary "pass fail" device whose strength is in determining whether the tube will work at all. The transconductance tester is somewhat more sophisticated in setting parameters at an operating point, which may or may not represent the actual application conditions that the circuit imposes on the tube. Some of the major issues in selecting a tube tester involve the configuration of sockets and socket adapters, and availability of test data for specific tubes. Also, the condition of the tube sockets has to be considered. The useful life of a tube tester was relatively short, because of socket wear. While the sockets could have been replaced, introduction of new tube types and socket configurations continued steadily into the mid-1960's, and replacement rather than repair of a worn unit was justified to support newer configurations. One must keep in mind that the vast majority of tube testers of both the emissions and transconductance type were sold and positioned in a prominent place in a point-of-sale retail business. They were uncommon in engineering and manufacturing operations. What faults can a tube tester find? Obviously, it will cull out tubes that are totally non-functional, such as those with open heaters. Tubes that light and conduct, but indicate either "?" or the high end of the "bad" range on a tube tester may function perfectly well in the actual circuit. The real problem comes when a tube tester indicates "good" but the tube won't operate properly in the application circuit. Hard faults are fairly easy to find in-circuit. The only really valid test for tube condition is in a test under actual operating conditions, and the device under repair provides those conditions at the application socket. The easiest and quickest test at the socket, beyond doing some simple meter and scope checks, is to plug a known good tube into the socket and see if that solves the problem. Even in a shop where sales policy required 100% testing of tubes in a tester, a significant percentage of tube replacements were for faults found in in-circuit testing involving tubes that tested "Good" on the tester. (The following was furnished by Dan Schoo) Q. Does anyone have advice for the make and model of the best tube tester for restoring and maintaining communications receivers I've seen units made by Hickok (600, 6000, others) as well as military (TV2C). What are the advantages/disadvantages of each? Thanks. There are many good testers available. A mutual conductance type is a better choice than an emission tester. Many times the choice is a matter of personal preference about the layout and cost. Hickok made many good instruments. All of them were of similar design and should work equally well. The 600A, 800, 800A, 6000 and 6000A were very similar. They were aimed at the radio/TV service industry and were designed to be easily transported. The 6000 is a nice machine but way overpriced in the current market. I'd take an 800A any day of the week over a 6000. The 800 and 800A used the meter to measure shorts/leakage instead of a neon lamp in that capacity. With the meter you could measure leakage to a much lower level than with the lamp. The only difference between them is the socketing. The 800A was updated to include Compactrons and Nuvistors but still retained the old sockets. The 500 series was a bit larger and not as portable as the 600/800/6000 but similar in function and about equal in performance. The top of the 500 series was the 539C which was closer to a laboratory type tester than the others. It had three meters and several features you might use in circuit design. It would test the firing voltage of VR tubes and small thyratrons. It tested for leakage with the meter but also had a neon lamp for fast short tests. The 700 series was larger too and more or less aimed at the industrial and communications market. These were a little classier than the other series but not as advanced as the 539. The best machine they made was the 700. This was closer to a TV-2 than any of the others. It was designed for laboratory use and had seven meters. If you are just doing repair and restoration on receivers any of the Hickoks will suffice. The 752A is a good choice because it has some of the desireable features for communications equipment like VR tube tests, has newer and older type tube sockets, and reads the leakage on the meter. The TV-2 is a big machine and for normal service work probably way more than you need. User Contributions: |
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