AM stereo website

Here is a website that is run by AM stereo supporters:

www.amstereoradio.com

The site contains history and information about AM stereo and links to where you can buy new AM stereo capable CD and Mini Disc players. It also tells you where you can buy AM stereo conversion kits and you can order a low-power AM stereo transmitter. Finally, you can also support the petition about the scarce availability of AM stereo radios to at least increase the chances of making the AM band into another high-fidelity solution in the future besides FM.

Chris O'Reilly,
via email.

Analog computers wanted

Years ago, I was involved with the now dead technology of analog/hybrid computers, without which at the time, events like the Moon landing could not have occurred. They essentially were general-purpose scientific simulators using op amp technology.

I am looking for any surviving examples of the smaller machines such as the EAI TR20, TR48, 480 or 580 desktop systems which every university and tech college used. Perhaps some readers might also be able to put me in touch with "analog" PC simulator software. I would also like any recommendations on good electronic design "freeware" for PCs.

Rod Cripps,
60 Herbert Street,
Parkdale, Vic 3195.

Dodgy power cord on vintage radio

I refer to the excellent articles on Vintage Radio by Rodney Champness. Page 90 of the August 2003 edition shows a radio with a 2-wire power cord. I would like to suggest that an approved 3-wire cord should be installed as part of the restoration of a mains-operated radio. Besides being a safety feature this could be mandatory under local regulations.

The electrolytic capacitors in this set would be nearly 50 years old. Again I would suggest it would be prudent to replace these as a matter of course with new ones.

Ted Baker,
Bathurst, NSW.

Comment: we have spoken to Rodney Champness and he agrees that he normally would have changed the cord in the course of restoration.

Valve preamp welcomed

Congratulations on the excellent article on the valve preamp in the November issue. I cut my teeth on valve circuitry and realise the extensive amount of research that must have gone into the design.

Hopefully the valve exponents will be satisfied. It is of little comfort to realise that an op amp equivalent would have taken up about half of the magazine space, used a lot less room, given much better distortion figures, produced very little heat and not needed the high tension voltage.

Chris Potter,
Kilsyth, Vic.

Query on valve amplifier distortion

That was an interesting article you published for a valve preamplifier circuit in the November issue, especially the B+ supply for it. As far as the distortion performance goes, haven't there been valve power amps with similar performance (Williamson 15W @ 0.1%) since the late 1940s?.

Mark Harriss,
via email.

Comment: both the Williamson amplifier and the Mullard 10/10 in the sixties claimed 0.1% or less and Quad, McIntosh and a few others would probably have made similar claims. However, it is doubtful whether that would have applied over the full frequency range and up to full power.

Running a Luxeon 1W star from 3.6V

I love your LED torch projects! I have been playing around with the 1W Luxeon. In my case, I wanted a light, long-life headlamp for bushwalking and camping. It needed to throw a long beam to illuminate the track and also a less intense beam for cooking and other camp activities.

Initially, I thought of the Picaxe. Using PWM and a transistor to drive the LED and a variable resistor to set the output seemed to be the answer. I found that I was limited to either four rechargeable AAA cells or three alkaline ones as a suitable power source because of the Picaxe's peculiarities. In the result, I had a clumsy unit that only just drove the Luxeon at 350mA. I also had an unreliable wired PC board that failed at the most inopportune times (eg, when I was perched on a ledge).

I gave up on that idea and drove the Luxeon directly off my Mobile phone battery (3.6V Li-Ion rechargeable). This works well and the battery drives the LED at full power when needed. I added a small white LED (drawing 20mA) for use in camp.

Your "best torch project" has made me aware that the heatsink I used was probably overkill and I will grind it down to reduce the size of my unit.

Henry Berenson,
Macgregor, ACT.

Loves the valve preamp

I loved the valve preamp. I'm now looking forward to a series of "Little Jim" radios with 3S4 audio valves and 67.5V "B" batteries which takes a week of wages to pay for!

It is great to see SILICON CHIP is moving ahead with the times.

Dick Smith,
Terrey Hills, NSW.

24V LED lights up vintage rail-motor

I was a little amused to read the reply to a query on the "Ask Silicon Chip" pages in the October 2003 issue. This stated that it is impractical to operate your LED stop lights from 24V.

Just to set the picture, I belong to the Rail Motor Society which operates restored NSWGR CPH rail motors commercially. At times, we park our vehicles in refuge rail sidings at stations when we stop for the night - Katoomba being one example. The signalmen like to see a red marker light displayed on the vehicle facing the outgoing road.

To operate our normal marker lights, which use 24V 25W GLS lamps, we could take over 12 amp-hours from our batteries over night. On cold Katoomba winter mornings, that much off the battery capacity can lead to great starting difficulties. So when I saw your LED stop lights in the March 2003 issue, I had the solution.

I made up the units using high intensity white LEDs from Oatley Electronics. These require about 3.5V at 20mA. To achieve this, from our 24V nominal supply, I used 430Ω resistors for each group of four. This gave the current I required and the resistors each dissipate about 0.2W. I also made up one light with high intensity red 2V LEDs operating at 26mA Each resistor in that unit only absorbed 0.4W, a total of 1.2W.

Our standard marker light normally has a BC lamp. So I used a normal BC adapter as the base for the LED array. The only catch was that I had to re-orient each lamp holder and adjust the polarity so that the LED array, when facing outwards (the only logical placing), had the correct polarity.

The standard marker light has a red glass filter that can be swung across and behind the lens when the lower handle is rotated. I made one lower marker (which is not now used for any standard indication) a dedicated redlight only. But after that, I made them all with white LEDs and we use the red filter glass when we require a red light (at the rear of the train).

Everyone is amazed at the results. The penetration of the white LEDs is more visible than from a standard incandescent filament. When the red filter glass is moved across, the result is also brilliant.

The others think I am a genius but it is easy to copy someone else. Thank you for a great idea.

Jim Lowe,
Heatherbrae, NSW.

Comment: your idea of using white LEDs is great but we still stick to what we said in the October issue because you have to allow for the very considerable rise in temperature in tail-light assemblies on hot summer days, particularly when the lights (brakes or otherwise) are on for long periods.

Alternative to paint stripper

Congratulations on the October project "A Dirt Cheap High-Current Bench Supply", using a PC power supply. Can we have more articles on the reuse of old computer bits?

There is an alternative to paint stripper for ungluing the ferrite transformer. The tape around the outside of the transformer can usually be removed with a knife. Ten minutes in boiling water will soften the glue, maybe 15 minutes for a larger transformer.

Peter Reed,
via email.

Digital TV farce

Like many of your readers, I've been following the "progress" of Digital TV broadcasting, albeit with the somewhat jaundiced eye of someone from the other side of the TV lens.

Over the years, I have been a somewhat harsh critic of "Those Who Would Reform Our TV Systems" (basically from the "Curmudgeon-Who-Actually-Knows" viewpoint), mostly irritated by the grossly over-stated benefits of adopting various proposals, combined with the invariably grossly understated cost and inconvenience of adopting them! The worst example of this would have to be the BMAC system.

When the first Digital TV transmissions were demonstrated about 10 years ago, I thought: "At last! Something with real benefits for both the broadcaster and end user!"

Well, it took the various broadcasting authorities a while but they've managed the almost impossible feat of messing up the introduction of Terrestrial Digital Television. To my mind, what should have happened is that all the current analog channels would have been simulcast on a special narrow band of frequencies, perhaps at the top of the existing UHF band.

Think of the advantages: because of the narrow bandwidth, you could use a low-cost, compact, highly sensitive and highly directional UHF antenna.

Instead, we have this absurd idea of fitting them in among existing TV channels, both VHF and UHF. "But," they said, "you can use your existing antenna!"

As we now know, this is mostly rubbish. I know quite a few people with digital set-top boxes and the only ones who could get all the digital channels straight off are the ones who get perfect analog reception anyway! I got some of them to work by resorting to the old installers' trick of carrying an antenna around the outside of the house, looking for a "sweet spot". But this was still an extremely tedious procedure, because you had to locate what seemed like a likely spot with an ordinary TV set first and then see if the digital tuner would tune in ALL the channels there, and quite often it wouldn't.

So in the vast majority of cases, it pretty much looks like you're not going to get Digital TV without a revamped antenna installation anyway and so the UHF narrow band option would have cost about the same and given far better results.

No doubt you've seen the recent news stories that Berlin has now switched off its analog TV transmissions and this is being touted as a triumph for Digital TV and the techno-savvy of the Germans and so on.

Actually, the vast majority of Berliners are still watching analog TV, now delivered by cable! The reality is that about 83% of Berlin households are connected to cable TV which carries both free-to-air and cable channels. There are some digital cable services but most of them are analog, similar to Foxtel here. Most of the people without access to cable are welfare recipients, so the government has provided such people with set-top boxes for free or heavily subsidised.

I would love to know how this is working in practice, since a lot of "low rent" viewers tend to use "rabbit ear" type antennas, which simply will not work with digital transmissions. Most people would rather a "ghosty" picture than no picture but Digital doesn't give you that option!

There are a lot of other aspects that get glossed over too. Very few households these days have just the one TV set and many have more than one VCR. Each one of these is going to need a set-top box and again, most people only have a proper antenna connection in the lounge, relying on pop-up antennas for bedroom sets and so on, so there are more sets that will be effectively put out of action.

I also think that digital set-top boxes are still ludicrously overpriced, considering what's in them. I can see in a few years' time that the average TV set will simply have a standard antenna socket and an ordinary VHF/UHF tuner module with a separate Digital IF and decoder section. There's not going to be any "revolution" in viewer habits; people who just want an el-cheapo no-frills TV from K-Mart will still be able to get one but capable of receiving Digital TV.

Keith Walters,
via email.

A long-overdue kick-along for digital TV?

A US appeals court has recently upheld federal regulations requiring television set manufacturers to install tuners that can receive high-quality digital broadcast signals in new sets starting next summer. The Federal Communications Commission in August 2002 ordered that digital tuners be included in new sets as part of an effort to jump-start the lagging transition to digital television, targeted for completion by 2007 but likely to be delayed.

The Consumer Electronics Association, which represents manufacturers such as Sony and LG Electronics which owns Zenith, had challenged the rules, arguing that the FCC lacked the authority to impose such a requirement and that the order was arbitrary and capricious.

LG might own the Zenith brand-name but there hasn't been domestic (US) TV manufacture in a many years since the Japanese and Taiwanese wiped them out. No wonder the courts don't give a hoot if it inconveniences the manufacturers and impacts their profits.

The interesting thing is that by making it compulsory and due to the size of the US market, they will be making digital TVs by the millions. That will bring the cost down to where any other standard will be infeasible to start manufacture and we'll probably all end up using these sets worldwide.

I don't think the small digital take-up in Australia will hold back the flood of a cheaper standard and the providers (studios) will need to be compatible with overseas formats, preferably without such hacks as standards converters.

I'm assuming that our standard is different from the US one? That was the way it was going last time I paid attention. Well, that's my opinion anyway, always supposing they don't try making region-locked TVs and add region coding to prevent grey-marketing.

Congratulations on the excellent LED torch in the November issue; I hope there's a kit available soon from someone. Unfortunately, also a big HISS-BOO at the valve preamp. Even if anyone is sad enough to build it, it will have been a sorry waste of paper and ink, in my opinion.

Paul Turner,
Burwood, NSW.

Multi-element TV antennas: are they a con?

On the 25th October, parts of Sydney were hit by a massive hailstorm. I live out near Penrith and we copped the full brunt of it.

Fortunately, my house sustained only minor damage, the worst being to the TV antenna. This is what's interesting. Because we're a long way from the Artarmon transmitters, something other than the usual "suburban" installation is needed. But rather than putting up a huge mast, I decided to try using a "deep fringe" antenna, on an ordinary mast. This worked pretty well except for snowy reception on SBS.

I then tried a separate "96-element deep fringe" UHF-only job. That didn't make a lot of difference with the Sydney SBS transmitter but I found that by pointing it at Wollongong, I could get a much better version of SBS, plus quite usable reception of their UHF versions of 2,7,9 & 10.

Well, the interesting thing is that after the storm, the antennas were a bit of a mess! One of the UHF antenna's two back-screens were on the ground, along with most of its directors. The VHF antenna had lost its two big VHF I reflector rods and most of its other elements were twisted around like a tornado had hit it. But when I tried turning on the TV, I found that it worked almost as well as it did before!

So what is all that fancy-looking ironmongery for? It smells to me like somebody's just making a fairly ordinary antenna and "decorating" it with a lot of fiddly bits that don't do very little! But how do you tell a "real" antenna from a fake, without actually putting it up on mast?

Adrian Kerwitz,
via email.

Comment: without comprehensive test equipment, a shielded anechoic (to RF) room or an antenna test facility, it is impossible to fully characterise any antenna, particularly one that is designed to cover a wide frequency range. The fact that your setup shows little change is no indication, since your TV has AGC to compensate for differing signal levels and the stations you watch may not be affected by the missing or damaged elements.

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