Electronics on the Cheap

by Philip Miller Tate

(A new member is inspired to write about his experience of the surplus market)

Everybody knows that there are lots of places selling 'surplus' electronic components at prices considerably less than retail, but many won't risk buying from them for fear of wasting their money or because they can't get exactly what they think they need. In my experience, there are lots of bargains available if you know what to look for, in amongst many items dressed up as bargains which really aren't. However, only by dipping your toe in the surplus market will you discover just how much you can save, and it needn't cost you anything like as much as you are currently forking out to retailers! Some of my friends and colleagues look aghast when I tell them I probably spend several hundred pounds a year on my hobby, but then again, my next-door neighbour plays golf and tennis regularly, and I have a fair idea of what that costs him!

It was about twenty years ago that I realised that if I came across a circuit that inspired me to experiment with it, by the time I had gone through the catalogues and written out the order for the components, and then waited a week for delivery, I'd lost the urge to build the thing. Clearly, the parts I needed, or near equivalent (I emphasise), has to be immediately to hand so that I could at least attempt a quick lash-up of a circuit. A few 741s, some 555s, some TTL; a selection of resistors and capacitors; maybe a few power transistors; switches and push buttons, LEDs, plugs and sockets. Many hundred pounds down the road (spent over twenty years, mind you), I'm pretty close to my ambition, thanks to cheap components, and about 90% of straightforward circuits can be put together whenever the fancy takes me.

With all due deference to Arnold Exley and his article in the December newsletter entitled "Why I Use Kits", this piece might have been called "Why I Don't Use Kits" - for the same reason that many of us don't, namely the cost! Many of the items can be purchased more cheaply ready-built, and come with a warranty to boot! Mind you, I'm not knocking the quality of Velleman kits (which Mr Exley recommended) at all, but they're not aimed at the hobbyist on a strict budget, nor those who like to 'tweak' their circuits a bit. Anyway, back to the 'bargain component' world; the first question has to be "what constitutes a bargain?".

The first rule is definitely to do your homework, and here may lie a few surprises. Let us start with an obvious target - the small-signal transistor. The current 'bog standard' small-signal NPN transistor these days is the BC549, which is just a BC109 that's grown up. If you build transistor circuits you probably get through a least a dozen of these per year. Looking through EPE and the catalogues reveals that ESR will charge me 11p each; Maplin 8p; Rapid will also charge 8p, but hold on, that's a BC549B, not a BC549C. Going to the back of EPE reveals a number of lesser-known companies with small ads, a few of which sell me 20 BC549s for 1. Now, they don't say which gain group these are, but As are pretty rare, so they are most probably Bs. This probably doesn't matter for most circuits, but you can always ring up and ask if necessary (although the call could end up more expensive than the transistors!). At 5p each, this looks like good value, but wait a second - if I go back to Maplin, I find that they sell the BC550C, which is much the same as a BC549C but less noisy, for only 6p, at which point the 'bargain' price doesn't look so good! But, looking a little closer at the small ads section in EPE, I discover Bardwell offering 30 BC549s for 1, and although these turn out to be BC549Bs, a just 3p each this is the bargain we've been looking for. Incidentally, Greenweld (the surplus Mecca) sell one-off BC549s at 12p each! This is not to say that Greenweld don't have real bargains - they certainly do from time to time - just always do shop around.

Other bargain buys might involve buying in bulk, but for cheap transistors this is unlikely to require an outlay of more than a few pounds. Twice in the last year or so, Greenweld have had a 'Million transistor sale' of surplus ZTX transistors at 1 for a pack of 50 of one type. The first time around I bought 50 of each of ZTX109 (small-signal NPN), ZTX500 (small-signal PNP), ZTX323 (RF) and ZTX450 (medium power NPN), plus some n- and p-channel MOSFETs just to experiment with. In this situation, you need a good transistor data book; "Towers" is probably the best but personally I prefer Babani's smaller and cheaper "Transistor Data Tables" by Steidle (BP401). Incidentally, when Greenweld had their second 'Million transistor sale', I was well-primed and in like a shot, only to find that they had already sold out of most of what I wanted! I still secured some useful Darlingtons and medium-power PNPs though.

Another way to buy transistors, though less common since the demise of Bi-Pak, is the mixed bag which you have to sort out for yourself. This can often offer something like 100 devices for 1.50 or so. Transistors are manufactured under such stringent conditions that it is extremely rare to find any failures, but bear in mind that you will probably get a fair sprinkling of less useful types such as low-gain PNPs and very-high-frequency switching transistors that are hopeless as amplifiers. Sorting these takes a bit of work and you need a good data book, a transistor tester of some kind, and a steady hand. On the other hand, I find that going through 100 transistors with a magnifying glass, a pair of tweezers and a transistor tester curiously relaxing and satisfying, often more so than getting circuits to work - now I understand why my father spent his evenings sorting his stamp collection! Failures being rare these days, any high-leakage measurements almost certainly mean having your tester set to NPN when the device is PNP (or vice versa), or an unexpected leadout arrangement. Incidentally, in almost 30 years I have never managed to destroy a transistor by (a) connecting it the wrong way round, (b) connecting the power supply the wrong way round, or (c) overheating it with a soldering iron. I have managed to break the odd lead off, though. Two golden rules of bargain price transistors; Greenweld (and others) will usually warn you if the leads have been trimmed. Personally, I never buy transistors with lead lengths less than 8mm, they're just too fiddly to be useful. Some of the cheaper packs may have 4mm leads. Secondly, never ever buy a pack of 'unmarked' transistors unless you have a comprehensive transistor tester to hand; you'll never find out what they are, and you may not find them very useful if you do.

Surplus ICs are another interesting area. Occasionally, bargain packs of old favourites like 741s and 555s are offered, and it's undoubtedly useful to have some around. A mixed bag of 74-series TTL might prove useful, but don't expect the one you want to be in there, and beware packs that are 90% buffers and line drivers; definitely not interesting. I bough 100 TTLs for 2, pretty useful, and 100 mixed ICs for another 2. I didn't expect to use them all! In the end, I identified about 85% of them and will probably use about 20%, but that still works out at 10p each, which is a good price for a small amplifier, op-amp or phase-locked-loop. Incidentally, if anyone can tell me what a ULN2283 is, I'd be so grateful if you would get in touch! (I've got 14 of them, you see!)

If you're looking for keen prices, you don't necessarily need to keep up-to-date with the surplus market; keep various different catalogues and compare them. All are not equal! In particular, Maplin prices for discrete components are typically about two to three times greater than, say, Rapid Electronics (ring 01296 751166 if you don't have their catalogue). This is disappointing as I was a loyal Maplin customer in their early years, living only a bus journey away from their first shop. There are some real surprises in the Rapid catalogue; some items advertised by Greenweld are in there but cheaper; battery prices are amazing! They'll sell you a PP3 for 50p; buy 20 (admit it, you use a lot of PP3s) and the price comes down to 36p each. Button cells that will cost you 1+ in the high street cost just 11p! Standard red LEDs cost 7p each, but get this - buy 100 and the price comes down to 4½p. Now, stop thinking "why do I want 100 LEDs?" and think that for less than a fiver you need never run out of red LEDs ever again! Rapid also very much live up to their name and will deliver next day without fail if you telephone you order through.

Resistors are not hard to find but it's getting difficult to find suppliers who will sell you less than 100 of any one value at a time. This usually costs about 1 but there are some place (I'm thinking Bardwell's again) that will sell you 100 for 45p if you're prepared to slum it and use 5% tolerance devices. I'm prepared.

Another recent example of a bargain relates to 'inside knowledge'. Last year, J&N Factors (alias the real 'Bull') sold off some Philip's Electronic Engineer add-on kits for 1, making it clear that these were useless on their own. However, I still have my Electronic Engineer kits from when I was a kid (the 60's if you must know) and I knew that each one had a very nice twin-gang variable capacitor worth a couple quid at today's prices. Seeing as how my son (hopefully) will want to build radios in a few years' time, I bought five. And it's not true that the kits are useless; each contains an RF transistor, two IF transformers and an oscillator coil, plus some capacitors and resistors that will enable you to make a simple 465 kHz BFO, or a variety of other RF oscillator circuits. J&N Factors also have a great range of mains transformers for a couple of pounds each.

Last summer saw something of a price war between J&N and Greenweld concerning small "gel" 12V accumulators manufactured by Yuasa, eventually coming down to 2.50 each. These are an almost ideal battery for many projects owing to their high capacity and available current, and ease of recharging, and at a price approximately one-sixth of retail. Incidentally, Rapid also sell a 6V version (about the size of a cigarette pack) for 5.50 which is probably the ideal power source for small vehicles and robots. Maybe I'll write an applications article on them at a later date...

Cheap electronics demands a little know-how and ingenuity; spotting the magic words "... or any general purpose silicon NPN transistor will do..." rather than tracking down a 2N2926Y transistor for your 1970s circuit, or not rushing out to buy a BC549B at 12p when a 2p BC171C will suffice; or being prepared to bend the leads of a higher-voltage capacitor than that specified; or ignoring the 6 printed circuit board altogether and re-designing the circuit on Veroboard (often to discover that you can make it smaller and neater that way...!).

Further to my comments above on the general reliability and toughness of transistors, I must admit to having recently destroyed a power darlington by deciding that a heatsink wasn't necessary just for a quick circuit test - wrong! Mind you, irritating though it was, the knowledge that it cost 25p instead of 1.50, and that there were three more in the box, meant that I didn't cry on that occasion - you see, I'd got it at a bargain price.