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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old Today, 10:15 am   #141
Radio Wrangler
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Default Re: Quad 11 test run

Yes, I think I listed three turrets to be linked together. put the earth clips of both scope probes onto them as well. That'll fix the problem and make the tests work.

David
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Old Today, 10:39 am   #142
julie_m
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Default Re: Quad 11 test run

The clue should be in the name. A word that ends in meter means an instrument for measuring something. A word that ends in scope means an instrument for viewing something. They're not necessarily the same thing.

A voltmeter gives you a nice accurate reading, but it takes some time to gather that reading in the first place and it can't change instantaneously (either because the needle takes some finite time to move; or because converting an analogue value to digital takes some finite time, and more if it's precision you want).

An oscilloscope gives you a quick and dirty guess -- or rather, it gives you lots of quick and dirty guesses in rapid succession, and draws a graph with time on the X-axis. Where something is changing too fast for a meter to respond to, that's important.

Given a DC-coupled amplifier with a 37V power rail, if you try powering it up with no speaker and no input signal, what would you probe the output with? If you use a meter, you might see 19.1V, spend too much time arguing over whether that was too high for the expected 18V5 and miss the real fault. If you use an oscilloscope, the first thing you might see is it's somewhere between 15V and 20V, which is certainly not egregiously out-of-range; but then if you see the trace suddenly going wild, you'll know for sure what is going on.

I'm personally convinced that much of the "anti-oscilloscope bias" is mostly for the sake of convincing the hater themself that they do not really need to own such an expensive, finicky instrument -- or that one within their budget can't possibly be any good. But times have changed; and you can obtain a 20MHz analogue instrument for next to nothing, or a simple battery hand-held digital one for not much more. And they are also easier to use thanks to automatic range and timebase selection and triggering. Of course such an oscilloscope will have limitations compared to a top-of-the-range unaffordable one; but it would have to be really lousy not to beat the daylights out of not having one!
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Old Today, 11:20 am   #143
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Default Re: Quad 11 test run

Quote:
Originally Posted by julie_m View Post
a top-of-the-range unaffordable one;
Even that's changed, Julie. Serious scopes are available cheaply. Sitting not too far from me is a Tektronix 465B in full working order..... 70 didn't break the bank. Tektronix is the rolls-royce of scopes. 100MHz, 4 channels, 5mV/div sensitivity, dual timebases and all sorts of tricks.

But is it suitable for a beginner? is a common question. Id doesn't appear so, but if someone gets shown how to set it up for basic measurements, it'll do fine. Then as they get more experienced and more adventurous they can try out some of the added bells and whistles but they still know how to drive the basic scope underlying it all.

If they'd gone for a very basic educational scope, they'd have soon hit its limits and had to change to a more comprehensive model and had to start learning all of that machine from scratch.

But the belief lives on that some instruments are too much. Too complicated, too difficult. I suppose it keeps the prices down for those of us not scared by them.

If I have seen further than others, it's because I've been standing on a pile of old test equipment... I must get round to fixing it one day

David
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Old Today, 11:40 am   #144
Ted Kendall
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Default Re: Quad 11 test run

I got into using 'scopes almost from the off - my first was a Panax with EF50s and a wonky timebase, but still useful in a way meter could never be. Why grope at a problem through a blanket when you can easily remove it and take a look?
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Old Today, 12:04 pm   #145
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Default Re: Quad 11 test run

Hi David, some years ago I was involved with a special truck mounted container for for Racal ,for radio com. use by the UK army. This was built on the Faraday principle, and all sorts of weird ideas were incorporated in the contruction.
Mike.
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Old Today, 12:24 pm   #146
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Default Re: Quad 11 test run

They might have called it Faraday, but I think they would have been really disappointed if it had been.

Electric fields are easy to screen, it's the magnetic fields which are real b*ggers. So you'll find an attempt to make an all metal seamless enclosure, doors close with knife-edge flanges plugging into spring-finger stuffed channels.

The idea is that a fully enclosing metal surface repels magnetic components by means of eddy currents.

To protect radio comms gear you need a real screen one that stops everything. A Faraday screen is not good enough, a faraday screen is one specially designed to let stuff through. Think of colendar when you want a pressure cooker.

David
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Old Today, 3:48 pm   #147
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Default Re: Quad 11 test run

Right David, did that test. With the probe on either U W X or Y no change from the a/c wave from L/T supply and other trace is this weird looking trace with like a sharp peak in it. These two traces stay the same all the time. I tried to take a pic, but sun is shining in at the moment. I may get better luck after tea.
Mike.
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Old Today, 4:17 pm   #148
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Default Re: Quad 11 test run

As a matter of interest,and now I am more confident using the scope, I have repeated GJ's test in post 50. Results are same as in that post with the exception of W is out of phase and U is in phase. Could this be that U and W have been tagged wrong and have been soldered in wrong turrets ?
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Old Today, 5:34 pm   #149
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Default Re: Quad 11 test run

It's beginning to look that way. I wasn't able to follow post 147, though.

David
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