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Old 9th Apr 2024, 9:45 am   #1
Essex Sight
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Default NATO Mk.1 Avometer

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Hello

I work for Essex Sight a charity helping visually impaired people. We have a NATO Mk.1 Avometer that we would like to know more about and possibly donate to a museum if there is likely to be any interest?

Any help much appreciated.

Jonathan
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Old 9th Apr 2024, 12:42 pm   #2
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Default Re: NATO Mk.1 Avometer

Jonathan,

As you will have gathered from the NATO title, this is a military version of a high-quality general-purpose instrument for measuring alternating and direct current, voltage and resistance (Amperes, Volts and Ohms). This particular version was designed principally for work on contemporary electronic equipment in the 1960s and 1970s. It was derived from a design which first appeared in May 1951 and was very widely used in UK industry and education as well as in countries which followed British practice - the Model 8 Avometer. Both the military and commercial versions were superseded by a different design in 1972 and made, with slight variations until 2008.

The Model 8 and its military derivatives were one design in a range of electrical instruments, especially multimeters, for various different applications, first introduced in 1923.

Your meter should have a serial number at the lower edge of the scale plate. This will be in the form xxxxx-mm-yy where 'x' is a serial number digit, 'm' is the month and 'y' the year of manufacture. This should be seen through the bottom edge of the glass.

These multimeters were manufactured in quite large numbers; the millionth Avometer was made in 1966, so there are still quite a lot about. They are quite long-lived and still quite widely used, mostly now by private owners such as the contributors to this forum.

The best price your are likely to get would be if someone near you with the necessary skills were to check over the meter and service it. It could then sell for a few tens of pounds depending on the demand at the time it was offered.

If you don't want to go to the trouble of preparing it and putting it up for auction, it's quite likely that a forum member might be willing to make an offer for it and I would expect this to be a fair refrlection of its value.

If you are interested in more detail, this site will give you the benefit of much fine work done by Richard Allan. http://www.richardsradios.co.uk/AVOmultimeters.html

If even that's not enough, let us know here!

PMM
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Old 9th Apr 2024, 12:53 pm   #3
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Default Re: NATO Mk.1 Avometer

Hi Jonathan,

www.richardsradios.co.uk is what might be termed a bible for avometers generally, but to summarise what you have there a military version of an Avometer Model 8 MkIII. It differs in certain ways but effectively does the same job. It's not rare as such, the ones that are still extant today have mostly been acquired through military surplus.

Condition is a bit of a lottery, some have been abused, some are basically sound and just need a bit of attention. In my humble opinion a museum is a bit of a last resort, but at least it's better than being drilled and made into a funky industrial look table lamp.

I'm not too far from you, as you're a charitable organisation it could be worth me checking out a) if it works and b) what state the battery compartment is in (people leave batteries in and they rot) This might help with decision of what to do with it.

Value of the meter is not great (see ebay for examples, many of which don't sell because they're overpriced)

(Edit- this post crossed with Peter's!)

Dave

Last edited by The Philpott; 9th Apr 2024 at 12:58 pm. Reason: typo
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Old 10th Apr 2024, 7:52 am   #4
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Default Re: NATO Mk.1 Avometer

The 30/100 scaling makes it an AVO 9, AVO 8’s of that period had 25/100 scales.

The 5A AC range, the lack of the 10mA AC and 600V DC ranges, and the plain English rather than international symbol markings, make it a Mk I, I think.

The metal plate on the back of the instrument should be marked with the Model type, although neither the back plate, nor the case it’s in, are totally reliable in this respect.

With the meter and case in good condition, and the genuine AVO leads it seems to have, it should fetch a few 10’s of pounds. You could use the meter to measure the voltage of a small battery as a rough check that the movement is working (this test doesn’t need a the battery inside the meter), and look inside the battery compartment to check for corrosion, to reassure potential buyers.

Stuart
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Old 10th Apr 2024, 8:35 am   #5
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Default Re: NATO Mk.1 Avometer

The NATO stock number 6625-99-105-7049 identifies it as the Mil Spec test set, also designated CT497A.

Basically it is a Mk1 (a Panclimatic model for use it aggressive environments) in the correct case for the NATO number, complete with test leads.

The Mk1 had different range divisions to the conventional Mk8II and III. The meter scales are also in a different order as compared to the Mk8 models.

The 6625-99-105-7049 (CT497A) was designated in the instrument list for field servicing of the Racal RA17 Mk2 and RA17L, EMER E724.

Craig
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Old 10th Apr 2024, 8:41 am   #6
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Default Re: NATO Mk.1 Avometer

I'd be quite interested in buying it by the way...

Craig
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Old 10th Apr 2024, 10:25 am   #7
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Default Re: NATO Mk.1 Avometer

Thanks Everyone for the information. The meter was part of a large bequest of Amateur Radio equipment from a gentleman we helped over the years. All of that has been sold, apart from three items - the avometer, a bathtub morse key and a military precision attenuator designed for laboratory/workshop/field use (kindly identified by Peter Marcham from Bletchley Park) which the trustees thought may have some historical or social value and perhaps should go on display somewhere. Clearly the meter is not at all rare and I appreciate that it is better to go to a collector. Here's some more photos.
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Old 10th Apr 2024, 10:27 am   #8
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Default Re: NATO Mk.1 Avometer

The battery compartment
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Old 10th Apr 2024, 12:07 pm   #9
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Default Re: NATO Mk.1 Avometer

We've seen far worse battery compartments, that'll clean up nicely.

Interesting how many meters have MOD stickers from around 1990-1992, it suggests there was a purge of old equipment shortly after this from (all) the armed services.

(I was aware of the 100/30 scale and the odd ranges, i left it out for simplicity!)

Sounds like you might have a customer Jonathan, (medium parcel of course as it'll be over 2 kilos) by the way it's well worth passing on those used 15 volt batteries with the meter, as they can be re-stuffed with upgraded button cells and resealed.

Dave
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Old 10th Apr 2024, 12:41 pm   #10
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Default Re: NATO Mk.1 Avometer

A good, complete package there with case and leads- I was never very impressed with AVO leads personally, but the tough leather case makes for good protection.

I, too, have one of these with very similar labels and dates- on a visit to Anchor Surplus in the early '90s, they had a piled-high warehouse crate of them in varied condition at a "lucky dip" very good price, I sifted through and found a cosmetically good one that also turned out to be electrically fine, a colleague was less fortunate in picking one that appeared to have suffered a major burn-up internally.

Yes, I prefer the 1-3-10 scaling- as well as appealing purely from the mathematical elegance point of view, it may have been more useful across nominal 24/28V systems. A 300V range is also useful with many low-power valve circuits.
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Old 10th Apr 2024, 12:45 pm   #11
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Default Re: NATO Mk.1 Avometer

Quote:
Originally Posted by Craig Sawyers View Post
I'd be quite interested in buying it by the way...

Craig
Great, you can pm me or email me on jonathan@essexsight.org.uk

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Old 10th Apr 2024, 1:52 pm   #12
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Default Re: NATO Mk.1 Avometer

Before I forget:-

Apart from being well packaged there's a simple procedure to protect the delicate moving parts from damage in transit-

Set the right hand rotary switch to DC
Set the left hand rotary switch to the lowest current range (which i think is 50uA)
Link the main red and black terminals at the bottom with any old bit of copper wire

If the meter is in good order, shorting out the meter movement in this way makes it very slow and lazy, and thus much less vulnerable to shocks.

Dave
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Old 10th Apr 2024, 3:00 pm   #13
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Default Re: NATO Mk.1 Avometer

Thanks Dave, much appreciated!
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Old 10th Apr 2024, 3:25 pm   #14
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Default Re: NATO Mk.1 Avometer

One post moved to a new thread here:-

https://www.vintage-radio.net/forum/...d.php?t=210161
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Old 11th Apr 2024, 2:47 pm   #15
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Default Re: NATO Mk.1 Avometer

Hi Jonathan and Dave - re. Post#12, I have discovered from experience that this meter protection mechanism is only effective if the cut-out hasn't tripped, as can happen due to mechanical shock in transit.

I haven't seen it mentioned elsewhere, but I would recommend taping down the cut-out button, as well as shorting out the meter terminals, and setting the appropriate range switches as recommended for each model, for maximum protection during courier transport.

Cheers
Chris
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Old 11th Apr 2024, 6:29 pm   #16
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Default Re: NATO Mk.1 Avometer

Spot on; hadn't thought of that.

D
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