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have them in stock, they may be able to transfer them from another one. At the time of writing, Mouser has the NJL3281DG transistors but DigiKey and element14 do not. The complementary NJL1302DG transistors are not in stock with any of those sellers, but they can be ordered, with delivery expected in May. If you aren’t so fussy about sound quality, the SC200 (January-March 2017; siliconchip.au/Series/308) is easier to build, has basically the same power and should still sound good. We can supply the PCBs and transistors for the SC200, although Altronics has a complete module kit available (Cat K5157). Advertising Index Altronics..................... 29-32, 51-54 Blackmagic Design....................... 7 Dave Thompson........................ 111 DigiKey Electronics....................... 3 Electronex..................................... 9 Emona Instruments.................. IBC Hare & Forbes............................. 15 Jaycar..................IFC, 11, 39, 68-69 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.............OBC Mouser Electronics....................... 4 PCBWay....................................... 13 PMD Way................................... 111 SC Ideal Bridge Rectifiers........... 95 SC PDFs on USB......................... 67 SC USB Cable Tester.................. 50 Silicon Chip Binders.......... 64, 111 Silicon Chip Shop............ 106-107 Silicon Chip Songbird.............. 109 Silicon Chip Subscriptions........ 55 The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 89 Next Issue: the June 2024 issue is due on sale in newsagents by Monday, May 27th. Expect postal delivery of subscription copies in Australia between May 22nd and June 14th. 112 Silicon Chip It would be possible to build an SC200-based amplifier and swap the modules for Ultra-LD Mk.3/4 modules later. The Ultra-LD modules are slightly smaller than the SC200 module and use the same heatsink pattern. The power supply requirements are identical. If you don’t need a lot of power, consider building an amplifier based on the Hummingbird modules from December 2021, although their performance is not quite as good as the SC200. The Hummingbird uses a lower voltage transformer; Altronics has a complete module kit (Cat K5158). 10kW ½W resistor attached to diodes D2 and D3 is changed to 15kW ½W. For resistors R1 and R2, use the values shown in the table accompanying the circuit diagram according to the DC supply the Loudspeaker Protector is connected to. RF preamplifier for oscilloscopes wanted I want to build the SiDRADIO (October & November 2013; siliconchip.au/ Series/130), but I can’t find the MMC capacitors. (T. R., Southgate, NSW) ● There has been a lot of confusion about the terminology regarding multilayer ceramic capacitors. The term most commonly used to refer to them these days is “multi-layer ceramic capacitor” or MLCC, but other terms have been used in the past, including “monolithic capacitor” and “monolithic multi-layer capacitor” (MMC). They are all essentially the same. All electronics retailers should have them, including Jaycar, Altronics and element14. The Jaycar and Altronics part codes for the values used in the SiDRADIO project are: • 1μF MMC: Jaycar RC5499 Altronics R2950A • 220nF MMC: Jaycar RC5494 Altronics R2935A • 100nF MMC: Jaycar RC5490 Altronics R2931 • 10nF MMC: Jaycar RC5480 Altronics R2910A Thank you for producing a great magazine. I have been a subscriber and buyer since almost the start. I want to build a detachable RF probe similar to the unit in the June 1988 issue (pages 72 to 74) and can source the 2SC3358 transistors. My requirement is probably 0.5-30MHz, mainly for checking oscillators in valve radios. Is there a later circuit that would be better, or using more modern transistors? I prefer through-hole components as they are much easier to handle. I am currently using a dip/wave meter built from an Electronics Australia circuit from the 1970s, but I want a more accurate frequency reading. (J. M., Wellington, New Zealand) ● You could consider building the RF Preamplifier circuit from Circuit Notebook, July 2009 by Dayle Edwards (siliconchip.au/Article/1507). The tuned circuit using L1, VC1 and VC2 can be deleted, and a 1MW resistor can be added to bias gate 1 of the Mosfet to ground. Apply the signal via a 10nF capacitor to gate 1. Alternately, the somewhat similar January 2004 Antenna & RF Preamp For Weather Satellites by Jim Rowe (siliconchip.au/Article/3326) might be of interest. Both circuits use some SMDs as dual-gate Mosfets are not readily available in through-hole packages. Loudspeaker Protector used at higher voltages Charging a Li-ion cell from USB I built your Loudspeaker Protector (October 2011; siliconchip.au/ Article/1178) from an Altronics kit (K5167). The instructions mention that 50V AC is the maximum voltage recommended for the AC Sense input; however, my transformer delivers about 54.5V AC. Is it safe to use the AC Sense feature with the slightly higher voltage? (M. K., via email) ● You can connect your transformer to the AC Sense input provided the I am looking for a kit to charge a 3.7V Li-ion battery from a 5V USB source. Thanks for your help. (R. J., Nambucca Heads, NSW) ● Modules are available to do that so inexpensively that we could not produce a design or kit to compete with them. For example, we sell TP4056 1A Li-ion charger modules in our shop for $2.50 each (SC4305 with a mini Type-B USB socket or SC4306 with a micro Type-B). SC Where to find MMC capacitors Australia's electronics magazine siliconchip.com.au