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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 7th Apr 2020, 2:00 pm   #1
astral highway
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Default Differential scope probes...

As a result of this thread: https://www.vintage-radio.net/forum/...d.php?t=165490...

I am looking for a pair of 'good enough' differential scope probes.

Looking around from scratch, they seem quite expensive, to , and I only need to do a few hours of testing. Or they are available as part of a portable digital oscilloscope, via the Chinese market. .

I am using a GWInstek GDS-1022 digital scope.

Before anyone jumps in with the suggestion of using the amplifiers in the 'scope to do an additive measurement with ordinary probes, this is not a reliable function on my 'scope and just can't result in a useable trace. But this is OT for this thread, just background.

I would be highly appreciative and really happy if anyone has anything like this they want to sell or any leads... (hahah!)

Thank you
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Old 7th Apr 2020, 7:44 pm   #2
chriswood1900
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Default Re: Differential scope probes...

Al
Differential amplifiers always seem to be expensive but assuming the problem is with earthing there are some alternatives. A while ago I had a small box that I used to do switch mode PSUs which used an opto-isolator and was powered by a 9v PP3 it had a about 500Khz bandwidth and allowed me to display the wave-forms in the PSU without shorting out or earth problems. The only problem is I can't remember the maker but it was from a small company in South Wales which had closed down. Whilst trying to find them I was reminded of this which may do what your looking for. https://www.elektormagazine.com/maga...-201409/27026/
I have not tried it but other Elektor projects have been good.
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Old 7th Apr 2020, 8:44 pm   #3
astral highway
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Default Re: Differential scope probes...

Hi Chris,

Thank you for this great suggestion. It's high time I registered with Elektor and I will do that and investigate.

It's such a shame that this niche company you mentioned had to close down, though.

Thanks again,

Cheers,

Al
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Old 26th Apr 2020, 6:37 pm   #4
chriswood1900
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Default Re: Differential scope probes...

Al
I did find the name of the company it Was Waugh Instruments Ltd and they must have been around from late 80s to mid 90s the last address I found was in Clywd although they were at Olney Bucks for a little while. The unit contains two amps one pre amp for the isolated side opto coupled to another unit to feed the scope. Sensitivity was around 10mV DC-1MHz with a feed of 100mV to the scope.
I'm not sure how many are around but a least we now know what its called.
They also made some other instruments including a scope calibrator and some other pre-amps.
The company was run by Peter Waugh who is cited in articles on isolation amplifiers.
If anyone knows any more I would be interested to find out.
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Old 26th Apr 2020, 9:53 pm   #5
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Default Re: Differential scope probes...

Waugh Instruments. Peter Waugh. A lovely man. I got to know him when he was at Olney. He previously was the designer at Scopex. He had a terrible accident when a car crossed the verge on a motorway. Smashed his legs. He was off work quite a while, and another director took over the design of the digital 'scope he was working on. A moving target at the time. Get a sample ram chip, before you place an order, it has been superseded by a better one. Anyway, the "stand-in" was not up to it, and went down a few blind alleys. The company went bust, Peter lost his home, the other directors escaped (good lawyers or contracts perhaps). Anyway, peter went to live in Wales. When they got there, his wife was diagnosed with breast cancer. I rang him one day, his son answered, saying his wife had died that day. I had visited him there a few times and never saw his wife (had wondered why) but I visited again later. He was producing his calibrator then, and the isolation amplifier, and I bought one of those from him. Don't use it much, but handy if needed. That uses a special probe, modified "normal" probe.
Later I was talking to him, and together with his son, he was building a light aircraft. Where he lived, at the top of a mountain in my book, he only had one take off direction, straight of a sheer cliff face. Anyway, he met a lady, they wed, and he went to live in France. I lost contact, and don't know if he flew the plane, or maybe his son did.
A very clever guy, very down to earth, and helped me many times.
Les.
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Old 26th Apr 2020, 11:20 pm   #6
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Default Re: Differential scope probes...

In addition to the Elektor probe (which has limited bandwidth, less than 60KHz) is this one I found while looking recently. Not so simple but appears to be similar to the probes that cost several hundred .

https://hackaday.io/project/169390-a...erential-probe

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Old 27th Apr 2020, 11:58 am   #7
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Default Re: Differential scope probes...

Les
Thanks for the background on Peter it was interesting and sad although hopefully he found happiness in the end.
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