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MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. Grateful for donated test equipment A few months ago, I sent you an e-mail about a BWD instrument I wanted to repair, and expressed interest in buying other BWD products. Thank you for publishing this for me. I have been given two oscilloscopes by your readers, for which I am very grateful. When I am too old, I plan to give my collection to Wireless Hill Museum here in Perth. So thank you for all you have done for me. Trevor Collins, Bellevue, WA. Giving away console radios & chassis As a keen reader of your fine publication, I have been engaged in electronics for the last 60 years. I have repaired and restored many valve sets and military equipment. As a result, a lot of ‘to do’ items have heaped up. With advancing age and deteriorating eyesight, things have come to a halt. Having lost colour perception and fearing high voltages, I have decided to call it quits. I have about two cubic metres of console radios and chassis. This includes a Tasma, a Stromberg-Carlson, an unusual Sanyo, Radiola and other chassis for fixing or pillaging. I would like the whole lot to go to a keen restorer. Should any of your readers be interested, contact me by e-mail to discuss details. Most of this gear is untouched. W. Schaaij, Broken Hill, NSW. pimschaaij<at>gmail.com in the April issue identifying the Test Master was good feedback. I am prompted to see if your readers can identify another piece of test equipment. I was given a Transistor Test Set (see photo below) which has no identification as to its source. It also has laced cabling, so it might also be a Telecom training exercise. Does the name ACE on the meter face have any significance? Probably not. The test set has a professionally-made front panel, but the squarecased meter seems to be a substitute for what could have been a circular-cased original. Also, the ADJ.Vgs knob appears to be from an AWA radio, not original. In David’s article, he also mentions that 10% of NOS (new old stock) KT88s are gassy. There is a trick worth trying with KT88s (and KT66s) that test gassy; let them run for 24 hours with only 6.3V heater voltage applied. This can sometimes restore them to a usable state. Many years ago, I designed test amplifiers using KT66s for AWA’s loudspeaker factory test rooms. After the annual factory Christmas holiday shutdown, when switched on for the first morning, the fuses would blow; gassy valves! I eliminated this by running the amplifiers with the rectifier valve removed the day before the factory resumed production in subsequent years. That warmed the valves without HT applied and drove out the gas, solving the problem. Mind you, that was only after a few weeks, not many years. Also in the March issue, in your “All About Capacitors” article (page 75), I believe I have spotted the first use in Silicon Chip of the correct SI prefix for high-value electrolytic capacitors; 68mF, not 68,000µF! Why do all manufacturers persist with non-SI designations? I still remember the days when a 1nF capacitor was designated either 1,000pF, 1,000µµF or .001µF. At least they have got that right! Ross Stell, Kogarah, NSW. Comment: many hoarders refuse to admit as much; kudos to you for doing so! The main reason we do not use Letter from an admitted hoarder Dr David Maddison’s article, “Hoarding: Urban Electronic Archaeology” was very interesting (March 2021; siliconchip.com.au/Article/14773). It appealed to me because I too am a hoarder. The response from two former Telecom apprentices in Mailbag 4 Silicon Chip Australia’s electronics magazine siliconchip.com.au GME Australia mF very often is that many people incorrectly use mF when they mean µF, leading to confusion; possibly this is because they do not know how to generate a µ symbol. GME (www.gme.net.au) is a privately owned company that designs, develops, manufactures and distributes worldclass radio communication equipment right here in Australia. We are proud to be Australia’s only manufacturer of UHF CB radios, with our state-of-the-art engineering and manufacturing facility in Western Sydney. Geekcreit LCR-T4 and germanium transistors Hiring Senior RF and Firmware Engineers And we are Hiring! We are always on the lookout for Senior RF and Firmware Engineers. Our Senior RF Engineers: → Develop RF circuitry, create specifications, select components, design schematics, and layout PCBs → Evaluate and test designs against specifications and for industry standards compliance (we have a selection of environmental test chambers, 3D printers and more!) → Ensuring compliance with all communication legislation and liaise with certification test houses → Preparing assembly and test documentation for the production team Our Senior Firmware Engineers: → Develop real-time code, digital signal processing, user interfaces, and communication protocols; all on modern 32-bit microcontrollers → Testing designs against specifications and for compliance with industry standards and user requirements It would be a big plus if you have any of the experience above, or are currently working in the Defence Industry. We have recently started designing for the Defence Industry and are seeking to complement our workforce with Engineers who are skilled in military communications design. We’d love to hear from you if you’re interested in either or both of these roles and especially if you have a keen interest in all things radios (we know you’re out there!) Please email your resume to: HR<at>gme.net.au Or call us on (02) 8867 6029 17 Gibbon Road WINSTON HILLS NSW 2153 6 Silicon Chip I have a version of the LCR-T4 Mini Digital Multi Tester that you reviewed (February 2021; siliconchip.com.au/ Article/14755) and, as you say, it tests many devices quite well. While not a problem for most people, my unit fails with germanium transistors, though. James Greig, Spring Gully, Vic. Comment: you are right; it does not handle germanium devices well. That is likely because their base-emitter conduction voltages are considerably lower than silicon types, and below its detection or operating threshold. Capacitors article was informative I’m just writing a short note to say how much I appreciated the piece by Nicholas Vinen titled “All About Capacitors” (March 2021; siliconchip. com.au/Article/14786). With no formal training in electronics, I have always fallen back on my high school physics description of two metal plates separated by an insulator. I don’t think I will even look at another capacitor the same again. From now on, I shall ask myself “what would Nicholas say about that capacitor in that application?” Keep turning out the great magazine. I don’t build too many of the circuits anymore but enjoy reading about them and the other various articles each month. Cliff King, Oxley, Qld. Tantalum capacitors prone to failure Thanks for the informative article on capacitors in the March 2021 issue (siliconchip.com.au/Article/14786). I have a few comments regarding tantalum electrolytic types. I had a recent failure (smokey explosion) inside a piece of commercial test equipment which involved 10μF 16V miniature bead-type tantalum capacitors. I had never had a problem with these before, and assumed them to be safe and reliable. But then I ran a web search for “tantalum capacitor failures”. Australia’s electronics magazine It appears that these devices can have a catastrophic thermal runaway condition leading to destruction and damage to nearby components if there is sufficient power supply energy. Otherwise, they fail short-circuit. This often occurs a short time after the equipment is turned on. The consensus for use appears to be that they should never be allowed to receive even a momentary reverse polarity voltage; should not be connected directly across a low impedance/high current voltage rails; should always have some series resistance to limit current flow in the event of failure; be operated at no more than 50-60% of their rated voltage; and must not be overheated when soldering. In my case, one capacitor was across the 15V supply and self-destructed with noise, light and smoke. The second capacitor was connected as a transistor collector bypass and fed from the 15V rail via a 10W resistor – it had gone short-circuit and toasted the 10W resistor. Ashley Smith, Flagstaff Hill, SA. Comment: We have also found that older style tantalum capacitors are not reliable long-term. Modern types are used extensively in computer equipment and do not appear to be a significant source of failures, although that might change as they age. If your list of restrictions were accurate, that would make tantalum capacitors pretty much useless. The main reason to use them is their low ESR value; hence, they are suitable for high-frequency bulk bypassing, where regular electrolytics are not. We normally use multi-layer ceramic capacitors instead, as they are superior in virtually every way. Only in a few specific cases are tantalum capacitors worthwhile, and in those cases, you usually need to use the expensive solid types to make using them worthwhile. March issue enjoyed S ilicon C hip March 2021 is a ‘bumper issue’! Super! Regarding the History of Videotape (siliconchip.com. au/Series/359), I learned my TV Studio engineering in Germany, with an RCA TRT-1, full of valves. “Statistically, one is dead all the time”, commented our instructor. I even mastered the art of editing (physically cutting) tapes by hand; it often worked. siliconchip.com.au Ready for Tomorrow We are constantly investing in our services and product range to make sure you are ready for tomorrow! A global electronics distributor that provides you with x x x x Local support Dedicated account management Quotes on volume requirements Not in catalogue sourcing x x x Contract Pricing Flexible scheduled ordering Exclusive buffer stock arrangements Contact us now Phone: 1300 361 005 Sales: au-sales<at>element14.com Quotes: au-quotes<at>element14.com au.element14.com/ready4tomorrow Helping to put you in Control PID Temperature Controller 230VAC powered N1030-PR Compact sized PID Temperature Controller with auto tuning PID 230 VAC powered. Input accepts thermocouples J, K, T, E and Pt100 sensors. Pulse and Relay outputs. SKU: NOC-320 Price: $81.00 ea Digital 4-20mA Generator EPM-3790-N can be used as a Control Panel For VFD Speed Controller. It has a 4-20mA output and a direction output which can be set by the front panel keypad. SKU: EEI-401 Price: $129.95 ea Digital Voltmeter Round Waterproof 3 Digit Red LED Round Voltmeter measures 5 to 48VDC. SKU: HEI-001 Price: $11.95 ea RS-232/422/485(TB) Modbus Gateway Modbus TCP to Modbus ASCII/RTU converter allows Modbus TCP masters to communicate with serial Modbus slave devices. Is fitted with Terminal block not D9 connector. SKU: ATO-159 Price: $269.95 ea Isolated Load Cell 2mv/V 0-10V Transmitter with Display Converts a signal for a 2 mV/V load cell to a 0 to 10 V signal. Able to power 2 load cells in parallel. DIN-rail mount. SKU: ALT-415 Price: $249.95 ea LabJack T7 Data Acquisition Module LABJACK T7 Multifunction DAQ with Ethernet, wifi and USB. Features 14 analogue inputs, 2 analogue outputs and 23 digital I/O SKU: LAJ-045 Price: $739.30 ea Ultrasonic Wind Speed & Direction Sensor RK120-07-AAC Economical Ultrasonic Wind Speed & Direction Sensor with Modbus RTU RS485 output and 4 metre cable. 12~24VDC powered. SKU: RKS-028M Price: $499.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Silicon Chip More details wanted on digital radio modes Thanks for the article on Digital Radio Modes in the April 2021 issue (siliconchip.com.au/Series/360). By the way, the correct spelling is Hellschreiber, not Hellshrieber. Despite that mistake, I found the article interesting. Perhaps you could also expand on HF radio data modes such as PACTOR and the more recent VARA (which works amazingly well with a PC soundcard). These modes offer quite high data rates on voice bandwidth radio channels. Horst Leykam, Dee Why, NSW. Comment: as you will see in part two this month, we mention PACTOR but not VARA. There are so many different encoding schemes that it is difficult to cover them all. Multi-amplifier module wanted Prices are subjected to change without notice. 8 Then the Bosch-Fernseh Quadruplex came along. It looked like a rebadged Ampex VR-1000A. The article explains things so well; I wish I had it 50 years ago! I’m looking forward to the follow-up parts. Then the Urban Electronic Archeology article by Dr David Maddison (siliconchip.com.au/Article/14773) reminds me of my outback electronic garage... And last but not least, Nicholas’ article about capacitors (all about – really!). That article must have taken years of research; a masterpiece (siliconchip.com.au/ Article/14786). I have several Sony shortwave radios, very nice ones at the time, but most of them died because of capacitor demise. The story goes that these radios (made in Japan) were made with capacitors from a container full of secondclass devices. It’s challenging to find the culprits, as desoldering the suspect caps is required. Strangely, other Sony gear (amplifiers, Betamax VCRs etc) didn’t suffer, only the radios – pity! My local radio repair shop refuses to repair those radios, but gave me an interesting hint. There is test gear (in kit form) that allows capacitors to be measured in-situ, without desoldering. How is that possible? Anyway, thanks for the great magazine. Hans Schaefer, Armidale, NSW. Comment: we’re glad you enjoyed that issue. The Videotape Recording series consists of four parts in total. Yes, in-circuit capacitor testers exist. They can be affected to some extent by other components in the circuit, but usually will give you good enough results to know if a capacitor has failed or not. We have reviewed some in the past, eg, the EDS-88A in our May 2013 issue (siliconchip. com.au/Article/3782). We aren’t sure if that device is still available, though. As for faulty capacitors, your story reminds us of the “capacitor plague”, which greatly affected computer motherboards and related gear in the early 2000s. We had an article on the subject in the May 2003 issue (siliconchip. com.au/Article/6644), or you can read more about it at https://w.wiki/39AD I sent you a question recently about the possibility of installing your SC200 amplifier modules (January & February 2017; siliconchip.com.au/Series/308) in place of Australia’s electronics magazine siliconchip.com.au the ETI series 5000 modules that blew up in my old amp. I’ve since been pondering changing my system over to an active crossover type, and was looking at your active crossover design from 2003. But building six separate power amplifier modules is a bit daunting, so I started looking around for a three amplifier mono module designed for active crossovers. I haven’t been able to find anything suitable. What I would like is a quality (stereo) amplifier like the SC200 for bass, a 50W or so for mid-range and perhaps a 20W amplifier for the tweeters, all on one board with a sub-board having the active crossover. The options that a multi amplifier/crossover like this would give to the DIY speaker builders worldwide would be enormous as the ‘black art’ of crossover design is eliminated. I know this can all be done with modules, but I’m not sure whether the lower power amp modules are of the same quality as the SC200, and I’m also not sure whether many would know how to lay out all the modules to minimise noise etc. Tony Brazzale, Bumberrah, Vic. Comments: low-power amplifiers aren’t much simpler to design or build than high-power amplifiers as they still need pretty much all the same ‘front end’ components. You could build SC200 modules but leave one pair of output devices off (and some of the associated components like the emitter resistors) to save a bit of time and money. Also, keep in mind that if you are building a system with a mix of low-power and high-power amplifier modules, you will probably need several different supply rails to achieve good efficiency. For example, ±57V or so for the 200W modules, and maybe around ±35V for lower power (50W) modules. That complicates the power supply and wiring. Another reason you wouldn’t want to run the low-power modules from the higher voltage rails is safety. If a lowimpedance load is connected (like a 4W speaker, or one with severe dips in its impedance curve), the current is no longer being spread between multiple output devices, leading to an increased chance of failure. Running those amps from lower voltage rails reduces the maximum current drawn. Another electricity saver scam I have just seen this advertisement for a “power saving” device called the Voltex. It is unbelievable. It’s even worse than electronic rust prevention. See https://getvoltex.com/ article4/au Bruce Pierson, Dundathu, Qld. Comment: it’s frustrating that this sort of scam is still around (see our previous debunkings of these devices, eg, in the November 2007 issue). There are only three ways to reduce what you pay for electricity: get a better rate, reduce your usage, or steal electricity. It is possible to reduce your usage by increasing efficiency (eg, getting a better-sealed fridge), but a box that plugs into the wall isn’t going to do that. They claim a 95% reduction in your electricity bill is possible, making the stealing electricity option the only viable answer as to how they achieve it... SC 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au