(24-04-2011, 04:30 PM)AlanBeckett Wrote: Joe,
I think that you can safely say that you succeeded in adopting a different style to David and his wooden boxes
When I was a lad the objective was usually to cram the works into something like a cigar tube. Do such things still exist? I guess the alternative for old codgers would be a Steradent tube.
Alan
Not everything I've made has had the 'wooden box' treatment!
I've been making stuff since when I was 12 in 1951, back when it was crystal sets and one valvers. My interest was further stimulated when later, I became a 'paper boy', and on my rounds I used to dawdle along and thumb through such delightful magazines as 'Hobbies Weekly' which often had simple radio articles, and later still, Radio Constructor. Thus, I was able to read the mags free, before the paying customers on my round were able to lay eyes on them!
I've attached a pic of a couple of signal injectors I made many years go - one in an icing syringe bought from Woolworths for a few coppers - the other in a felt tip marker pen. The one in the syringe dates back to 1959, and is still going strong. I could have used two 'Red Spot' surplus transistors (out of spec - ie, low gain) at ten shillings each (50p) but decided to push the boat out and use Mullard OC44s at eleven shillings each (55p). It might not seem to be much of a decision for what seems to be a modest additional outlay of 5p each, but to put it into perspective, 50p in 1959 equates to £8.50 now, and 55p equates to £9.40, so a pair of OC44s in 1959 cost me the equivalent of £18.80 today! Still, it was a sound investment which has paid for itself many times over in fault tracing over the last 51 years since I dug deep into my pocket.
The later injector - about 1985, used a couple of BC108s, which I doubt cost more than 20p each, but even that equates to 64p each in today's money, yet we can buy 20 for a pound nowadays.
The icing syringe injector was built on perf board, the pen case one was built 'ugly style' or 'dead bug style,' with the components wired together on very short leads to make it compact. Neither are pleasing to they eye, but both are functional. I've attached a couple of scope traces to show the waveforms. I haven't bothered to check the frequency, but I imagine that it will be 1kHz to 1.5kHz or thereabouts, rich in harmonics to a much higher frequency so RF/IF stages can be checked as well as AF.
Hope it might amuse and interest someone out there!
Fo anyone who might wish to build a combined signal injector/tracer, there is an excellent Veleman kit - the 'K7000' available from the main stockists of Velleman Kits - ESR Electronics. It's on a neat PCB, with two on-board pots, one for the injector output, the other for the AF volume. It cost about a tenner. Highy recommended. You'll find it at the link below, an a PDF of the comprehensive construction manual:
http://www.esr.co.uk/velleman/products/index_kit.htm
The spec is:
Velleman K7000 Signal Tracer/Injector Kit:
Features:
• Injector:
• 0-2.5Vrms output (adjustable)
• Output impedance: 1.5Kohm
• Frequency: ± 1kHz
• Tracer:
• 3.5mV to 10Vrms sensitivity (adjustable)
• Gain: 40dB
• Input impedance: 50Kohm
• Output power: 0.5W / 8ohm
• Power supply: 7-9VAC or 9-12VDC / 150mA
David
