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Old 19th Dec 2017, 11:19 pm   #1
RadarAl
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Default Oscilloscope Practical Wireless August 1973

Back in 1974 I built the oscilloscope featured in Practical Wireless August 1973. I have since downloaded a copy of this edition. Does anyone have the following editions which cover more of the build or errata which usually appeared after. I was thinking of rebuilding one.
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Old 19th Dec 2017, 11:49 pm   #2
David G4EBT
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Default Re: Oscilloscope Practical Wireless August 1973

If you go to the link below, you'll find almost every issue to Pratcial Wireless to view, print, or whatever, including the issues you're looking for:

http://www.americanradiohistory.com/...s_Magazine.htm

Hope that helps.
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Old 20th Dec 2017, 12:11 am   #3
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Default Re: Oscilloscope Practical Wireless August 1973

I had a look at building this about a year ago. Not sure of any errata but I found some particularly horrible mistakes on the schematic. Design is relatively sound however.
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Old 20th Dec 2017, 8:31 am   #4
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Default Re: Oscilloscope Practical Wireless August 1973

I have the issue's that cover the Elektor scope if you'd like a look and I think ETI did a scope too.

Andy.
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Old 20th Dec 2017, 11:35 am   #5
David G4EBT
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Default Re: Oscilloscope Practical Wireless August 1973

The PW 'Student 'Scope' article was covered in August and Sept 1973 PW, and the Sept issue corrected some errors that arose in the first part. I've checked up to Jan 1979 and no further corrections were published in the 'Kindly Note' section, where corrections were published if there were any.

I recall considering building that 'Student 'Scope' but was put off by the fact that it only went up to 40kHz, so was OK for audio, but not much else. In fairness, it was made clear that it was a basic scope, hence it's name. It was built on 0.15" spaced perf-board (not 'strip-board') 17.75 inches long x 3.75 inches wide, rather than a PCB. To my mind, it was from the 'bodgertronics' stable, so I passed it by, hoping something with a higher spec akin to a commercial 'budget' scope might come along. It did, in 1978 - the P.W. 'Purbeck', which ran from Apr - Sept 1978 with a follow-up in Jan '79.

I successfully built the 'Purbeck', which goes to 5 MHz, and still have it.

It was quite a complex and costly thing to build even though I made all my own PCBs for it, as well as the metal cabinet. Luckily, for the most part, the PCBs consisted of rectangular shaped pads, so lent themselves to being traced onto 'Fablon' self-adhesive plastic, cut to shape with a modelling knife. That saved a lot of the expense, rather than buying the PCBs. I started to build the follow-up Purbeck dual-trace add-on unit, but found a Gould OS300 in the skip at work, which had apparently only been dumped as it was 'time expired'. It served me well for about ten years, till I sold it when I got a Hameg 203-7.

Have fun if you do build the 'PW Student' scope - it used just transistors - no long since obsolete ICs, so should be do-able.
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Old 20th Dec 2017, 11:50 am   #6
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Default Re: Oscilloscope Practical Wireless August 1973

Indeed. I think the most difficult thing to find is the transformers

Edit: incidentally looking at the schematic again, the main problem with the bandwidth is trying to extract way too much gain from the vertical amplifier in too few stages. I reckon adding another stage or two of modest voltage gain with relatively high current biased modern transistors between the boostrapped follower on the input and the vertical amp would give you a couple of MHz at least. Also it's a single ended amplifier. If it was differential right from the follower, it would be better.

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Old 20th Dec 2017, 12:04 pm   #7
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Default Re: Oscilloscope Practical Wireless August 1973

The spec says 40kHz max timebase frequency, bandwidth DC to 1MHz.

Lawrence.
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Old 20th Dec 2017, 8:56 pm   #8
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Default Re: Oscilloscope Practical Wireless August 1973

Hi Gents, there was also an excellent simple scope in WW in the 70's. It used cheap transistors and a couple of simple op amps. I used it as a project for the electrical apprentices.

If anyone is thinking of building one of these I may have suitable transformers and tubes available, PM me.

Ed
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Old 20th Dec 2017, 9:59 pm   #9
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Default Re: Oscilloscope Practical Wireless August 1973

Quote:
Originally Posted by ms660 View Post
The spec says 40kHz max timebase frequency, bandwidth DC to 1MHz.
Thanks Lawrence.
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Old 21st Dec 2017, 12:29 am   #10
RadarAl
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Default Re: Oscilloscope Practical Wireless August 1973

Thanks everyone for your quick replies. I hadn't noticed any mistakes on the circuit diagram, could you point them out please.
I would be very interested in seeing some of the other magazine projects which you mention.
High end performance of the scope isn't a problem. I am not building a stand alone scope but rather incorporating it into a project I am building, a radar simulation interface. It will be used to monitor 420Hz calibration signals and 105Hz sine/cosine receiver antenna alternator signals prior to feeding them into the radar timebase.
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Old 23rd Dec 2017, 7:49 pm   #11
RadarAl
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Default Re: Oscilloscope Practical Wireless August 1973

The Sept 1982 Wireless World 'Low frequency Oscilloscope' looks quite interesting.
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Old 23rd Dec 2017, 11:02 pm   #12
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Default Re: Oscilloscope Practical Wireless August 1973

I bought a PW Student scope which had been quite well assembled at the Preston amateur radio rally in about 1977. It came with Aug and Sept 73 copies of PW. I got it working. For some reason I had a query about it and wrote to the PW editor who stated that "it was not one of PW's best designs".

The main reason was that it was a published design on Veroboard so had all sorts of stray capacitance reducing the bandwidth. I recall increasing the value of some collector resistors to give wider timebase sweep which increased the bandwidth a little, but I remember the trace eventually curving into a loop at the highest settings!

Nevertheless, it was my first major project and undertaken while I was at Northern Counties Radio School. Oh, happy days...

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