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Advertising Index AEE ElectroneX........................... 34 Altronics.................................75-78 Analog Devices............................. 9 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes............................... 5 Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 7 Ocean Controls........................... 10 PMD Way................................... 111 SC SMD Test Tweezers............ 109 Silicon Chip Shop............ 106-107 Silvertone Electronics................. 65 Switchmode Power Supplies..... 11 The Loudspeaker Kit.com.......... 67 Tronixlabs.................................. 111 Vintage Radio Repairs.............. 111 Wagner Electronics....................... 8 around Q1-Q4 would help to diagnose this fault further, but given that they are inexpensive devices that are relatively easy to replace, if you can’t find a soldering problem or component value error in that area, you could just replace all four. wide. This can also damage the ignition coil that could arc over internally and short out the windings. That fault is more difficult to check; the easiest method is to swap the coil and see if that fixes it (after checking the IGBT using a resistance meter). Jacob won’t climb his ladder anymore Modifying EA Active Crossover frequencies We bought our son a Jacob’s Ladder kit for Christmas. We separately bought the coil recommended in this kit. Upon original completion, the kit worked fine. While using it, it stopped working and has not worked since. We asked the retailer about this, and they agreed that we had built the kit correctly. Still, they were concerned by the age of the kit on their shelves (which they stated may have been there for many years) and the possibility that components may have dried out over this period, leading to the failure. Do you have any experience with regards to which components regularly fail? (G. D., Redcliffe, Qld) ● Electronic components sitting on a shelf should not fail after less than ten years. The only parts that are likely to age significantly are electrolytic capacitors, and we have plenty of 30-plusyear-old electros that are still fine. Modern electrolyte formulas handle ageing much better than much older devices. The semiconductors, resistors etc will definitely still work. Check fuse F1, which may have blown. The most likely failure is the IGBT (Q1). Usually, when these fail, they end up with a short circuit between the gate and collector (left and centre pins) or the collector and emitter (centre and right pins). The IGBT is most likely to be damaged due to the spark gap being too I recently came across several Twoway Electronic Crossover kits I started assembling about 10 years ago that I would like to complete. They were sold by Altronics, Cat K5570. The problem is that I have lost the instructions that came with them. Also, they were initially designed for crossing between mid-high and high elements. I would like to use them for crossing over at 100Hz. Can you suggest the component values required for sub-bass applications? (M. O., Croydon, NSW) ● Those kits are based on the Active Crossover for 2-Way Speaker Systems project from Electronics Australia, May 1992. A scan of that article is available for purchase from our website (siliconchip.com.au/ Shop/15/6072). To change the crossover to 100Hz, the component values can be scaled using the original crossover frequency versus resistor value tables. You can change the 2043Hz value to 100Hz by multiplying the resistor values by 10 and the C2-C7 capacitor values by 2.043. So R2-R4, originally 39kW, become 390kW and R5-R7 become 470kW (from 47kW). The original 2.2nF capacitors can be 3.9nF in parallel with 560pF (4.46nF total, within 1% of the required value of 4.49nF). Capacitor tolerance (typically at least ±5%) will be the main cause of frequency shifts from the required crossover frequency. SC Notes & Errata Vintage Radio, February 2022: the 100nF capacitor directly below the 6K8M valve in Fig.8 should connect to the GND rail instead of the AGC line. In that same figure, there’s a 33μF 600V HT filter capacitor missing from the 250V rail to GND. USB Cable Tester, November & December 2021: in the circuit diagram, Fig.1 on page 30 of the November issue, the numbers for pins 8 and 10 on IC1 are swapped. Pin ANE2/RE2 connecting to USBU-GND via a resistor should be pin 10, while pin ANE0/ RE0, connecting to USBU-ID via a resistor, is actually pin 8. The April 2022 issue is due on sale in newsagents by Monday, March 28th. Expect postal delivery of subscription copies in Australia between March 25th and April 15th. 112 Silicon Chip Australia's electronics magazine siliconchip.com.au