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Old 16th Oct 2017, 6:23 pm   #1481
Phil G4SPZ
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Default Re: AVO Multimeter survey

Hi Ted, that Air Ministry meter dates from June 1943. The original battery would have been a square section "Battery, 1 1/2 volt, No 11" which had a knurled terminal at the top (positive) and a flying lead for the negative. I have one of these ex-WD batteries dated 1962, and there was a later Ever Ready equivalent but I can't remember its number right now, 1662 or something like that, but they haven't been made for decades. So on the Model D, the fixed spade-type terminal is the positive, and the screw terminal which accepted the flying lead is the negative. A neat arrangement can be made using a single 1.5 volt D cell in a holder connected by soldered leads.

The Model D only has two working ohms ranges, 1K and 10K. The two switch positions pointing to the words "use on K=2" are not connected.
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Old 16th Oct 2017, 7:29 pm   #1482
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Default Re: AVO Multimeter survey

Thank your for the information Phil. I know the type of battery, they were in common use when I was in the army a long time ago. Some of lads made dirty DC chargers using a diode and I think transformer, to perk up the batteries powering their little Philips radios bought, when on leave in Cyprus. I'll get around to testing the Model D soon checking all ranges as I go. ted
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Old 16th Oct 2017, 8:16 pm   #1483
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Default Re: AVO Multimeter survey

I can photograph an instruction plate if that's any help. Richard's radios has a photo of the text on the rear also.

You probably know this already, but- don't try to turn the Q adjuster on the front. (They are dummies, glued in place at the factory.)
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Old 16th Oct 2017, 8:24 pm   #1484
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Default Re: AVO Multimeter survey

....When fitting a modern C or D cell holder situate it away from the walls enough for the sides of the holder to be able to flex for battery removal/insertion. I didn't- and had to
re-do it!
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Old 16th Oct 2017, 9:22 pm   #1485
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Default Re: AVO Multimeter survey

Model D- Well this is the appropriate text in a legible form, but i'm afraid the camera isn't coping with doing a full screen version without blurring.

This is quite a robust meter but the high voltage windings may well have gone open circuit by now. Good luck!
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Old 17th Oct 2017, 1:49 pm   #1486
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Default Re: AVO Multimeter survey

I had a batch of reproduction Type 'D' instruction plates copied from an unused one a few years ago.

These are very difficult to tell apart from the original. Please send a private message, if you would like one, £3.50 plus postage. I'll need to find some hardboard for protective packing so despatch may take a few days.

Ted,

I'll email you some data in the next day or so when I catch up with life a bit.

PMM
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Old 18th Oct 2017, 5:13 pm   #1487
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Default Re: AVO Multimeter survey

Just bought my first AVO Meter. It is a Model 8 MK I think. Serial No: 4684-C-452. It came with a set of probes.
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Old 19th Oct 2017, 11:11 pm   #1488
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Default Re: AVO Multimeter survey

OTF96,

That serial number is correct for a Model 8 Mk I, of April 1952 - 11 months after production began.

PMM.
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Old 25th Oct 2017, 6:54 pm   #1489
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Default Re: AVO Multimeter survey

Have managed to buy an Avominor Model 1A at last. It is in the post, so watch this space for progress. The repair will be an interesting one, let's just say that.
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Old 27th Oct 2017, 8:16 pm   #1490
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Default Re: AVO Multimeter survey

Universal Avominor s/n 132232-1155. Model 1A

The serial number is misleading- from what i gather the Model 1A usually has a different series of numbers, running up to at least 3,400 units. The serial 132232 suggests this meter has been (probably erroneously) included in the Model 1 production number series.

There has been a modification to enable the meter to be used as a miniature 'steampunk' LED desk-lamp powered from a normal USB socket, but the rarity of the meter means i am reversing this mod and returning it to it's original use. The former owner is kindly supplying a few small parts that were removed.

It bears Marconi Intl.Marine markings, and i am encountering corrosion in the brass wander plug ports.. spinning 600 grade wet&dry in them is (unusually) not having the desired effect- so i am now considering chemical attack. (suggestions please!)

As far as the drilled hole in the casing goes, i am considering my fave mix of araldite and black acrylic paint, or possibly milliput. (Again, suggestions welcome.)

To use the Low Ohms range, we short the NEG and 20,000 OHMS ports, and adjust for zero. The resistance under test is then put across 2.5mA and 500mA ports. Clever! I have powered it up and it works as accurately as the High Range.

Despite the magnetic shunt being at minimum setting, a test input voltage of 4.1v gives accuracy- the magnet hasn't deteriorated at all, for once. It may, of course, have been ever so slightly over-powerful at the start of it's life, and run down slightly over the decades to give accuracy in the 21st Century. I had wrongly assumed that the movement was going to be completely shot- which wouldn't have been a problem as it is the standard Model 1 assembly.
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Old 27th Oct 2017, 8:41 pm   #1491
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Default Re: AVO Multimeter survey

Dave, could you possibly post a full-frontal photo of the Model 1A, please? An interesting and rare instrument.
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Old 27th Oct 2017, 9:48 pm   #1492
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Default Re: AVO Multimeter survey

Hi Phil, given it a go-

In current conditions this is the best i can do- it's a bit like trying to get a photo of Captain Scarlet..

This anomalous meter looks to have crept under the radar to a great extent- perhaps as the visage is only distinguished by the use of 'THOUSANDS' at the top left of the scale, (quite similar to a Model 2) and of course by the additional LOW OHMS scale hiding under the 5V AC gradations. What other oddities are out there!? Fascinating.

Latest idea for attacking dulling/verdigris/dezincing inside the terminals is clamping the tail of a 3/32" split pin in a cordless drill, cutting it's head off and smoothing away the burrs, then trapping/wrapping the wet&dry into the split pin in the manner of a halfords cylinder bore de-glazer. I think i prefer this to acid.

Better pics to be sent to Richards Radios after i have restored the thing to how it should be.

Dave
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Old 27th Oct 2017, 11:00 pm   #1493
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Default Re: AVO Multimeter survey

Fascinating indeed! Personally, I've always found that a smear of Greygate 'Paste Polishing No 5' on a cotton bud twirled by hand inside the brass sockets to be most efficacious in cleaning tarnish from those hard-to-reach places.

Thanks for the pics. I don't have a Model 1A myself, but I have definitely seen references to the "low ohms" range on the Universal AvoMinor yet not seen such an instrument. Until now!
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Old 29th Oct 2017, 11:22 pm   #1494
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Default Re: AVO Multimeter survey

Additional: (Avominor Model 1A)

On a hunch i tried the '3 lead' procedure detailed in post #1490 on a bog standard Model 1 meter, and it reproduced the functionality of the LOW OHMS range to a good level of precision. I would tentatively say, therefore, that the only difference between Models 1/1A is the provision of the special scale plate (and the modified instruction plate.)

This might explain why the serial number on my meter is not as i expected.

With care there is the potentiality to update the Model 1.. but of course more than one scale shape was produced so a direct scan and re-print of my scale plate is unlikely to suffice for all movements!

In my experiment, a 15ohm resistor lined up with a fraction over 2vAC, and a 100ohm resistor lined up with 4vAC.

Dave
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Old 4th Nov 2017, 6:16 pm   #1495
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Default Re: AVO Multimeter survey

Avominor Model 1A - Now assembled back to original spec.

1- As a USB toadstool style desklamp
2- Hole filled in side
3- Large hole in top filled, next to 'MIMCCO' logo
4- New fly-leads attached & 2 resistors replacing o/c 25v bobbin
5- Shunt board/battery holder salvaged from a broken Model 2, wirewound resistors bolted to it after old copper rivets drilled out.

Needle was straightened and rebalanced, dirty switches cleaned, one threaded boss inside had split and was cyano-acrylated together successfully.

continued-
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Old 4th Nov 2017, 6:43 pm   #1496
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Default Re: AVO Multimeter survey

Continued-

1- more detail of instruction plate
2- instruction plate
3- improved image of front
4- scale plate detail. labelled 'Type 3' which is probably the scale shape.

There was a lot of (high resistance) verdigris and dezincification inside the wander plug ports, and one test lead had actually verdigris-ed through completely. This, together with the 25v bobbin being o/c, may have led to the meter being deemed useless and thus being converted into summat else.

New 3d printed feet are good, as is sometimes the case a thin sliver had to cut from one side of the rear ones, to avoid them catching on the instruction plate as it is opened. (A problem that could arise with the original feet.)

If anybody ever has the wish and technology to make a few Model 1A scale plates from worn out Model 1 plates, by all means PM me and get a better image from me on email, (but send me a couple of examples when they're done, eh?!)

Another meter saved, anyhow!

Dave Philpott
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Old 7th Nov 2017, 11:11 am   #1497
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Default Re: AVO Multimeter survey

Dave,

Some would call you stupid, but others including me way down under and of vintage years, rate you as a hero. Those that do not understand can get stuffed. LOL

Special regards, Trevor.
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Old 7th Nov 2017, 6:57 pm   #1498
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Default Re: AVO Multimeter survey

Thanks Trevor, that means even more coming from the country with a reputation to be able to make/invent/mend just about anything!

Overall this has become a very useful international archive, and if i can stick a few notes in here and there it lifts my mood no end.

I also tried the 'low ohms' trick with a Model 2 and with a Type E....neither of which co-operated. There was a little change in deflection, but not enough to be of any use.

Dave
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Old 8th Nov 2017, 6:06 pm   #1499
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Default Re: AVO Multimeter survey

Well the model D has a few problems, got the battery sorted, nothing at all on the Ohms ranges though. Had it out of the case and it looks a bit of a mess, 4 point contact diodes in stead of the correct rectifier. All DC voltages are OK so the movement is working I did check for accuracy. The needle zipped across rather quickly, could it have a damping problem? I can't imagine how, but I'm sure Phil or Dave will have the answer. I could do with a good clear picture or photo of the resistor layout if any one has one. No hurry as I have plenty of other jobs in the pipe line, pleased to say. Ted
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Old 8th Nov 2017, 6:23 pm   #1500
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Default Re: AVO Multimeter survey

Hi Ted, damping is relative, if you are used to a Model 8 or 9 with a graceful movement, the Model D does zip up the scale by comparison. As long as it reads consistently and zeroes consistently it's ---probably--- okay.

Was it a pic of the little board that relates to the resistance ranges that you wanted? I have a loose one with original (but scorched) windings on that i can take pics of, also i took some during restoration that show various parts of the innards (Mainly the windings)
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