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Old 19th May 2023, 7:39 pm   #81
russell_w_b
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Default Re: Old or New multimeter?

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Originally Posted by G6Tanuki View Post

I've never liked stuff like the AVO8; they always seemed too big and clunky to me. You can't put one in your pocket!
No... But you can keep screws, washers and other take-to-bits items in the meter glass recess!
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Old 19th May 2023, 9:51 pm   #82
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Default Re: Old or New multimeter?

Quite-we've all done it and it does no harm- but ensuring the pointer reading is honest should be done by rocking the meter on it's tripod feet, not tapping the glass!

Dave
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Old 15th Jun 2023, 11:05 pm   #83
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Default Re: Old or New multimeter?

I use a Simpson 260-6 since 1978 works great
It still made today itis a life time investment by one for life.

Dave

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A couple of decades ago there was an article in, I think, the old IEE journal "Electronics & Power" with a title something like "Precise, But Wrong" where the author recounted some of his troubleshooting experiences. One was a complaint from a customer who had bought a dozen or so precision voltmeters and complained that, when checked against their voltage reference standard, they were all out of spec. When he went in person to investigate, he found that, to save time, all the instruments had been connected to the standard in parallel, thereby lowering the resistance presented to the standard. When connected one at a time, all the instruments were in spec.
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Old 16th Jun 2023, 5:57 pm   #84
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Default Re: Old or New multimeter?

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I have very fond memories of my old TMK multimeter from work in the mid 70's. I had to purchase it from the alarm company I worked for .... it was about £15.00 which was deducted from my wages at £1 per week. If it broke, the company would arrange for repair FOC.

Best range was the 10 DC Amps which was useful for load testing the old carbon zinc batteries, especially the 1.5V flag cells.... anything reading below 3 amps would not last until the next quarterly inspection so was replaced.

It also had a rage for testing AC Ripple which was useful for testing PSU's.


Rog
I have a TMK 500 which I bought new around 42 years ago (from the now defunct "Bond & Mason" electronics shop in Stockton on Tees) as a youth and which got me through countless repairs and many hours of learning for maybe 15+ years before I went the way of the DMM. I've just dug it out, blown the dust and cobwebs off it and given it a basic try out and it still works Also found a Robin analogue meter (seems decent) which I'd utterly forgotten even existed! I have an AVO 72 in a cupboard somewhere which certainly worked when last used.

I'd love an Avo 8, just 'cos it's an Avo 8 and everyone involved in electronics should have one I have 2 or 3 that have been donated over the years but all have a fault which renders them BER. Namely a sticking meter movement on 2 of them. IIRC the third has lots of charcoaled bits where it must have been connected to a high voltage low impedance source such as 415V mains on a very wrong range...
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Old 16th Jun 2023, 6:23 pm   #85
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Default Re: Old or New multimeter?

I had a rare case of the input resistance of a DMM being the source of measurement error just a couple of months ago. I'd designed and built myself a high voltage bench supply for use with valved equipment and a "USP" is quite high precision (not really necessary of course to be able to precisely set a valve HT supply to within 1V or better and have it stay put to within a couple of mV over hours but the way the design was going naturally lent itself to it and I hadn't the capacity to resist).

Voltage dividers for the three ranges were calculated and suitable resistors dug out but to get ultimate accuracy I allowed for a SOT resistor to make up for tolerances etc. A temporary preset was employed to find the best SOT resistor and as a final/sanity check the divider output was measured and referenced against the measured output voltage. Well there was a discrepancy wasn't there... just maybe a couple of percent ish but seemingly unexplainable and it had me virtually pulling my hair out! Then a eureka moment as it dawned on me that the 10M input resistance of the multimeter was having enough effect on the measured voltages from the dividers (which are made with resistors in the 100's of K region) to cause the discrepancy.

I'd got just so used to ignoring the Input Z of a DMM as it's so high as to be negligible... except when it isn't!

I went back to my spice simulation and made allowances for the 10M of the meter so I knew what I should be reading on the meter when allowing for this and all's well
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Old 16th Jun 2023, 10:46 pm   #86
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Default Re: Old or New multimeter?

Jez, might the AVO 8's suffering a sticking pointer merely have ferrous fragment/s obstructing the movement..? - a problem that a steady hand, a head torch and a set of jeweller's loupes can rectify?

Dave
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Old 16th Jun 2023, 11:48 pm   #87
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Default Re: Old or New multimeter?

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Jez, might the AVO 8's suffering a sticking pointer merely have ferrous fragment/s obstructing the movement..? - a problem that a steady hand, a head torch and a set of jeweller's loupes can rectify?

Dave
It's possible Dave yes but it's years since I've dragged them out hence the "2 - 3 Avo's"... not even sure how many I have! I vaguely think 3 and one was totalled as above plus had a seized meter and the other one/two at least one had a sticky needle such as a ferrous particle would cause and the other either the same or seized completely. I could be wrong any or all counts there!

The internet is so full of both apocrypha as well as good info but I vaguely recall reading that in cases of a sticking pointer on an Avo 8 you would be incredibly lucky or skilled to ever get it back working as it should (some esoteric but believable reasons were given IIRC) and that it was a fools errand to even try... which sounds vaguely ridiculous reading that back but the guy seemed a real expert on Avo 8's .... IIRC!
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Old 17th Jun 2023, 12:03 am   #88
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Default Re: Old or New multimeter?

..I reckon on 2 out of 3 sticking pointers being fixable, either by aforementioned debris removal or backing off one of the jewels slightly.

The remaining 1 out of 3 usually seem to be down to a damaged jewel, and require watchmaker skills and a donor meter... most of us (including me) wouldn't even try. I assume this is the scenario said expert was referring to.

I agree there is a lot of flannel on the 'net. 'Cool your home down in 90 seconds with this brilliant new hack' etc etc.

Dave
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Old 17th Jun 2023, 1:11 am   #89
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Default Re: Old or New multimeter?

"Blah blah resetting jewels blah blah only a few in the UK can properly do it" seems somewhat what I remember yes! Like I say it was years ago when I had a quick look at them and then googled it.. we're talking 2000 or XP I'd have googled it with!

All the talk of analogue meters then mention of a TMK meter and my remembering that was the brand I bought as a lad and wondered if it still worked (I dug it out and tried it. it does. And Ohms could be still be zeroed on the higher ranges with the battery that's prob been in for at least 15 years.no not the original!) and it got me thinking about the Avo 8 and how everyone in electronics should have one by law etc and that I actually had a few I'd not looked at for years...

So many projects going on (whether for me or customers) and so few round tuits
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Old 17th Jun 2023, 2:42 am   #90
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Default Re: Old or New multimeter?

Most time you do not here on DMM or other
electronic volt meters about is the refresh rate.
This because they a slow computer for calculations for voltage and ohms. . Worst on low end DMM than high end high cost.

About the only time use a digital meter is checking resistors.
Everything else is the good old Simpson 260.

Dave


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Originally Posted by stickfly View Post
.... This struck me today when I was thinking of some problems I have with a vintage AVO meter : When you have a problem with a vintage multimeter & you have to take measurements, do you use a vintage multimeter or a new Digital meter?
i.e. I have a problem with an AVO Model 7 Mk2. Should I use one of my other AVO's for testing components etc, or should I be using a modern digital meter. Stupid, I know, but I just feel that it would be wrong to use a digital meter, but would the digital meter be more accurate ? Or does it really matter.
I think I'm just getting old I work in the photocopier industry & our apprentice said " What the hell is a multimeter "
Regards ..... Gary
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Old 17th Jun 2023, 10:18 am   #91
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Default Re: Old or New multimeter?

That is indeed a relevant point: Sampling Rate and Refresh Rate. Certain Auto ranging DMMs also take a long time to make an initial decision- my Uni-T meter is like this on Ohms and Volts. I don't actually mind, but i can see how it would grate on people doing repetitious tests in a hurry.

Dave
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