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signal ranges or it is only triggered by the ranges put out by the subwoofer amplifier? If you connect it straight into a signal source, would it flash for all frequency levels? Secondly, instead of using one 12V neon tube, would it be possible to connect eight 1.5V LEDs to the unit? Thirdly (and this is just to confirm), any 12V DC power supply should run it, right? (D. C., via email). • You really need to refer to the complete article to under­ stand the function of the circuit. We can supply the back issue for $7.70 including postage. As designed, the circuit will not respond to frequencies above 100Hz but by reducing the 0.1µF capacitor at the collector of Q1 you can improve this. However, the circuit and the neon tube itself inherently do not have a fast signal response - it’s really only intended for bass frequencies. You could connect a string of LEDs but you need a limiting resistor to set the current. By the way, most LEDs have a voltage drop across them of around 2V so you could only use about five, after allowing for the series limiting resistor. Yes, you can use any 12V supply. Mailbag – from page 25 said why? No wonder you give up after a while. I’m unable to recall how often on a new installation a 3-phase blower motor runs backwards; we all know that swapping two phases will make the motor rotate correctly but why is it sup­plied in the wrong rotation? I’ve no doubt there are excellent electricians out there, but I despise an organisation that allows the bad apples to remain and reject those who don’t do the apprenticeship but have Notes & Errata Simple Superhets, April 2000: the circuit on page 61 has an error. The grid of the 6GW8 triode should be pin 1, not pin 3. Ultra-LD 100W amplifier, March & May 2000: to eliminate a notice­ able thump from the speakers at switch-off, we recommend that the 100µF capacitor connected to the regulated -55V rail be increased to 220µF 63VW. Digital Voltmeter For Cars, February 2000: when using the volt­meter with 24V vehicles, the five 820Ω resistors will become quite hot. To alleviate this problem, we recommend replacing the 820Ω resistors with 10 1.8kΩ 1W resistors. Five can be installed on the PC board in place of the original 820Ω resistors. The other five can be installed underneath the PC board. Alternatively, use a 150Ω 10W wirewound resistor external to the voltmeter in place of the five 820Ω paralleled resistors which should be replaced with a short or link. The 10W resistor must be placed on the metal chassis of the vehicle using a suitable skills and at least a much better appreciation of AS3000. What really scares me nowadays is we are now letting these bad apples perform communications work and I’d be pretty sure that adherence to mandatory separations between mains and comms is frequently disregarded. I’m sure you all recall that GPOs used to be available with integral TV sockets until one day when an unsuspecting person was killed while attempting to rotate his aerial. These are illegal now and in effect was prior recog­ nition that some electricians cannot clamp and the connections insulated. The wiring should be clamped to the chassis to prevent breakage from the resistor leads. Low Distortion Audio Signal Generator, February & March 1999: the published PC board (01402992) shows a short between the 0.18µF capacitor on switch S2 and the adjacent shield track. This was due to a glitch in the conversion from the original Protel file to an HPGL file required for publishing. The overlay diagram on page 64 of the March issue shows the pattern correctly without the glitch connection. The Protel files sent to PC manufacturers were cor­rect. Also the 12kΩ resistor connecting between the LDR1 and VR3 should be replaced with a parallel combination of a 560kΩ resis­tor and .0047µF capacitor. Some constructors are using 3000mCd red LEDs for LED1 and LED2 with improved results. VR6 can be changed to 1kΩ to improve the ease of square wave output adjustment. be trusted to properly terminate and protect signal from mains cabling. On my last approach to the Electrical Workers Board, I let them know my background and offered to undertake any courses they considered would raise my skill level to enable myself to be registered as an electrician. The response was “it really doesn’t matter what you do or don’t know, the only way in is through an apprenticeship.” For similar reasons to the previous correspondent, please do not publish SC my name. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. August 2000  91