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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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27th Jun 2017, 8:43 pm | #21 |
Dekatron
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The swing of a needle vs accuracy and direct readout
I eventually found a meter with both analogue and digital readouts. The analogue readout is a true, moving coil meter/needle, not an LCD attempt at the same. It's a Mastech M9704 and it's a fantastic meter in many ways actually. As well as the normal V, I and ohms ranges it has capacitance with a nice couple of slots to place the cap in, and measures temperature and tests transistors - very versatile. The meter is housed (fixed) in its own protective case and the front of the case is designed to attach to the top of the meter to prop it up at 45 degrees for viewing. The leads are fixed and stow away in the case. Interestingly, when the meter is set to measure ohms, the meter swings to FSD, then comes down to zero when the leads are shorted; the opposite of an AVO.
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28th Jun 2017, 12:18 am | #22 |
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Re: The swing of a needle vs accuracy and direct readout
The Avo EA113 i'm using just now on the bench has an ohms scale with infinity at FSD and zero ohms in the pointer's rest position. Select Ohms and the pointer swings to FSD, short the probes and the pointer comes down to zero, as you describe yours does. There's a lot of AVO types
David
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28th Jun 2017, 7:35 am | #23 |
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Re: The swing of a needle vs accuracy and direct readout
I may be strange but I have no problems reading trends from a DMM. Still my favourite meter is an HP427A analogue though. It's as good as a 2000 count digital on any scale and despite being 51 years old it is perfectly in calibration. Unlike a traditional VOM it is FET based so has constant impedance in all ranges which is quite important if you want to use an RF probe.
The Fluke 8024B I have has the best continuity tester made by man though. |
28th Jun 2017, 11:01 am | #24 |
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Re: The swing of a needle vs accuracy and direct readout
I struggle with moving coil meters because they have their own ballistics that aren't standardised (unlike audio meters like PPMs). As I think was expressed earlier, a scope is better for changing signals - with the added bonus that it will show things no meter can, like parasitic oscillation or narrow spikes. Against that, nearly all 'scopes are earthed, and can't (easily) be connected to high energy circuits, so sometimes needs must.
I presume the M9704 was found second-hand? From a quick look, I can't find it for sale new anywhere. It certainly looks interesting, and if they were cheap enough I'd pick one up to test and review. |
28th Jun 2017, 11:22 am | #25 |
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Re: The swing of a needle vs accuracy and direct readout
Mark, yes it was second-hand off the auction site. I'd been looking for some time for such a beast. I use the swing of the needle to give me an idea of 'what's going on' (especially wrt DC voltages), and I use the LCD for a finite value. I've only ever seen the one for sale. I paid £30 for it.
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28th Jun 2017, 11:32 am | #26 |
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Re: The swing of a needle vs accuracy and direct readout
First hit on google!
£100 from Amazon, so not cheap. Enclose a picture of one of my Fluke 8000A/BU Small analogue indicator next to LED display. A bit too small to be of much use though! Peter
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28th Jun 2017, 11:52 am | #27 |
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Re: The swing of a needle vs accuracy and direct readout
I came across this ad in a 1977 edition of WW. Made by Sanwa, it seems to use a conventional movement but with an LCD scale that shows only the range selected. Nice idea - but given that LCD technology was pretty new at the time, I wonder how good it was?
There are (or were) a few on offer on the net, but they looked pretty sad!
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28th Jun 2017, 11:54 am | #28 | |
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Re: The swing of a needle vs accuracy and direct readout
Yes, I saw that but immediately disregarded it at that price. Those sellers are clearly sitting on old stock. I wonder what it sold for when it was in production?
Quote:
Interesting though - I have an 8000A, but hadn't realised that an analogue meter was an option. Thanks for sharing Last edited by mhennessy; 28th Jun 2017 at 11:56 am. Reason: Added quotes as another post appeared... |
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29th Jun 2017, 6:07 pm | #29 |
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Re: The swing of a needle vs accuracy and direct readout
The miniature Avo LR ohmmeter of ww2 vintage has infinity at FSD. I seem to recall one of the US made analogue meters does...the RCA Voltohmyst possibly.
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29th Jun 2017, 6:15 pm | #30 |
Nonode
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Re: The swing of a needle vs accuracy and direct readout
There's a bloke does the rallies with re-furbed AVO's and I always end up looking at the little Avo Minors. Lovely little things, especially the 60's ones.
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29th Jun 2017, 7:05 pm | #31 |
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Re: The swing of a needle vs accuracy and direct readout
The 'Minors i 'dig' the most are the Universal ones from the late '40's and early '50's.
They give rise to negative comments from a lot of present day users, but i think this is largely down to lack of maintenance, unrealistic expectations, abuse and lack of understanding. When they are fettled i find they are actually pretty viable for some jobs even now. |
29th Jun 2017, 8:22 pm | #32 |
Nonode
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Re: The swing of a needle vs accuracy and direct readout
The only thing that puts me off the earlier Minors is the 1000 -ohms-per-volt sensitivity. It's a bit low for many applications. I may treat myself to a used 60's one at the next rally, just for 'tuning up' and other trends. Watching digits flapping about like a fruit machine makes me fall over!
On the other hand, a cheap Chinese Special would probably be good enough....
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29th Jun 2017, 8:55 pm | #33 |
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Re: The swing of a needle vs accuracy and direct readout
A lot of what-I-do involves not taking an absolute fixed-voltage/current measurement but rather adjusting things to get a peak reading.
[think peaking crystal-oscillators, chains of frequency-multipliers and subsequent RF power-amps] For this, digital meters are hopeless - they take ages to settle to a stable reading after each few-degree tweak of a capacitor or inductor 'slug'. My analog-meter-of-choice is a 45-year-old "Taylor" 30KOhm/volt taut-band beastie. It's travelled the globe with me and so far has never let me down. OK, some people enthuse over AVO8s and the like, but my Taylor's a fifth of the weight and volume - which can turn out to be important when you come to check-in your baggage at some obscure airline's desk. Also, I've seen some AVOs that have been woefully-inaccurate. I wouldn't buy a secondhand AVO8 unless it came with a calibration-certificate from a UKAS-accredited test-lab. AVOs can look good but cosmetics don't always reveal their impact- and G-force history! For digital meters I go with the cheapest-and-nastiest £10-from-Ebay Chinese stuff. For the money they're surprisingly accurate, and again for the money I don't worry about leaving one behind hooked to some piece of gear with an instruction that "when you have the problem text me the numbers shown here...." |
29th Jun 2017, 8:58 pm | #34 |
Octode
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Re: The swing of a needle vs accuracy and direct readout
Maplin used to sell a digital multimeter that had, in addition, an analogue meter needle that traversed in front of the digits. Good for showing a trend.
I've got one somewhere but I've just checked and Maplin no longer sell it. Peter. |
29th Jun 2017, 10:40 pm | #35 |
Dekatron
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Re: The swing of a needle vs accuracy and direct readout
Universal AC/DC avominor even less sensitive @ 400 ohm/volt.. Surprisingly difficult to kill, though.
Model 2 is a bit more sophisticated at 4kohm/volt but servicing of any kind is a lengthy task, and the survival rate of the movement is not too good. Having seen a few tired AVO8's they certainly communicate quite well as to what is ailing them; and if just old age rather than abuse it's often those pesky leaf switch contacts. My favourite DMM is Farnell DM131 (and i'm not even sure why. Perhaps it's the internal construction.) |