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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
Does it display believable readings in voltmeter mode?
When connected to a 12V battery charger with a 21 watt bulb as ballast, it reads 8.5V, my DMM reads 9.17 (there could be a voltage drop due to high resistance in the terminals)
The same circuit gives 1.2 amps on both the AVO and DMM.
I'll set up a better test with a car battery in the morning.
(It's only a cheap 4 amp battery charger.)
I'd suggest testing the voltmeter function against ordinary AA 1.5 V cells, rather than introduce the unknowns of a car battery charger into the mix.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
. I'd suggest testing the voltmeter function against ordinary AA 1.5 V cells, rather than introduce the unknowns of a car battery charger into the mix.
using a brand new 1.5V duracell LR20 and a 3Ohm nominal resistor (3.3 according to my DMM) it reads 0.5A and 1.45V (but I've not fixed the 'suspected' problem of resistance at the terminals.)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
. I'd suggest testing the voltmeter function against ordinary AA 1.5 V cells, rather than introduce the unknowns of a car battery charger into the mix.
using a brand new 1.5V duracell LR20 and a 3Ohm nominal resistor (3.3 according to my DMM) it reads 0.5A and 1.45V (but I've not fixed the 'suspected' problem of resistance at the terminals.)
That sounds promising, and suggests you don't have a 'sticky' meter movement, an often serious fault. Once you've got your bad connections sorted out, you could do what you can to test the meter on every switch position, as multi-pole rotary switches are very vulnerable to corrosion, man-handling, and the effects of time.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
. That sounds promising, and suggests you don't have a 'sticky' meter movement, an often serious fault. Once you've got your bad connections sorted out, you could do what you can to test the meter on every switch position, as multi-pole rotary switches are very vulnerable to corrosion, man-handling, and the effects of time.
I only bought it to strip down and look at the concentrator. It's already cost me more in batteries than I paid for it, and I haven't replaced the leads yet (apparently RS still sell them)
EDIT: I've got the ends of the leads and the terminals soaking in Sainsbury's cola, not as good as 'the real thing', but it still contains phosphoric acid.)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
. That sounds promising, and suggests you don't have a 'sticky' meter movement, an often serious fault. Once you've got your bad connections sorted out, you could do what you can to test the meter on every switch position, as multi-pole rotary switches are very vulnerable to corrosion, man-handling, and the effects of time.
I only bought it to strip down and look at the concentrator. It's already cost me more in batteries than I paid for it, and I haven't replaced the leads yet (apparently RS still sell them)
Invest your time and efforts into reconditioning an Avo and you'll have a useful piece of kit to help you on your way for years to come.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Ash Small wrote ...
Proud Mary wrote ...
. That sounds promising, and suggests you don't have a 'sticky' meter movement, an often serious fault. Once you've got your bad connections sorted out, you could do what you can to test the meter on every switch position, as multi-pole rotary switches are very vulnerable to corrosion, man-handling, and the effects of time.
I only bought it to strip down and look at the concentrator. It's already cost me more in batteries than I paid for it, and I haven't replaced the leads yet (apparently RS still sell them)
Invest your time and efforts into reconditioning an Avo and you'll have a useful piece of kit to help you on your way for years to come.
But I've accepted a challenge to build a 25uA FSD movement. I can't back down now!
EDIT: BTW, apparently the movement in an AVO is 35uA FSD, and the lowest range is 50uA, at least it is on the Mk III
Registered Member #3567
Joined: Mon Jan 03 2011, 10:49PM
Location: USA, 1960s
Posts: 260
I would suggest just buying a good used 70's Fluke.
While the meter you have is great, it isn't ever going to be too accurate. (Stupid voltage drop) A good hamfest $50-75 fluke will last forever and have more than a 20k per volt impendence. (Correct me if I'm wrong, I'm just using the standard for meters) The chronic display problem is solved by taking apart the display and cleaning the contacts with alcohol. Mary, what is your opinion on this?
PS Try using Navel Jelly, it is basicly gelled pho. acid and pink too! It is great as a rust remover and dosn't have the temptation to be eaten.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Nah wrote ...
I would suggest just buying a good used 70's Fluke.
But I've accepted a challenge to build a 25uA FSD movement. buying one isn't an option.
I do have some 'pure' phosphoric, but it's 200 miles away. Coke is the next best thing. (after Naval jelly)
PM, you are correct, as usual, 37.5uA, not 35uA. (I was going to post in the morning (in the cold light of sobriety) that I have the utmost respect for yours, and Sulaiman's and Nicko's opinions (Wait til I post details of the other stuff I picked up when I collected the AVO, I'm sure you'll have plenty of advice).
This thread is, as I said before, 'just a bit of fun', but I don't really want to strip a perfectly good meter if I can find the relevant info elsewhere.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
I do have some 'pure' phosphoric, but it's 200 miles away. Coke is the next best thing. (after Naval jelly)
Tesco sell a phosphoric acid based stainless steel cleaner spray called Viakal, and I often use it for pickling copper and brass to expose a fresh surface, which it does very well.
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