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Old 7th Apr 2016, 10:41 pm   #1341
pmmunro
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Default Re: AVO Multimeter survey

Palmerino,

Thank you for the pictures of your meters, all of which are very interesting. You have found, like several others here, that Avometers are very addictive. You have gone to a lot of trouble to set up the equipment needed to service Avometers, so I don't think you will ever recover from your love of Avometers.

It would be of great interest to know more about the Samar M.U.1, such as when it was made, how many might have been produced and if this model was available on the commercial market or if it was made only for the armed forces. The range of products listed on the Samar website is enormous and very varied. I would think that a significant part of their range may be bought in but it is still a very impressive range with many unusual items, though sadly no Misuratore Universale. Do you know if this was their only Avometer copy or could there have been other models too?

The rheostat of the early (DC) Avometers is probably results from the origins of the Avometer design. This was due to Donald MacAdie, who was born in the far north of Scotland and, by the time of the patenting of the Avometer in 1922, was the manager of the Post Office Telephones factory in Holloway in North London. At that time it was common to test the pick-up current of electromagnetic relays and the rheostat function of the meter would have been useful for this. Using a suitable current supply, the rheostat could be adjusted to the point where the relay operated or released and the current read directly from the meter. I have no direct evidence that this was the exact intended purpose of the rheostat, but it seems quiet likely. (If anyone has instructions for adjusting telephone relays of the 1920s which would support this I would be interested to know).

The cross at the centre of the resistance scale of the 13 range Avometer is essentially a calibration mark and a 200 ohm internal resistor provided as a reference.

A scan of the English language instruction plate for this meter is attached. In paragraph 2 of the resistance range instructions, the correct term "pointer" is used but in paragraph 3, the incorrect term "needle" occurs. That's doubly bad practice because two different words are used for the same item.

PMM
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Old 7th Apr 2016, 10:59 pm   #1342
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Default Re: AVO Multimeter survey

Richard (Barmead),

Thanks for the information on your Model 7 Avometers. If the serial numbers were one contiguous range, there were 2154 Model 7s made between March and July 1948. Assuming there was a full 5 months between them, that's about 108 meters per week.

As your photographs don't show the earlier movement, can you tell us which kind it is please, either one with a horseshoe or a block magnet? It was around this time that the change was made and it would be useful to know more exactly.

There was quite a variety of resistance types used in Avometers, especially in the 1940s. The bobbin or spool wound type was used for many more years although gradually replaced by component resistors as these became available in consistently high stability types. However, the only real drawback of the bobbin wound type wound have been cost as it takes time to wind and calibrate them and the wire is expensive. They are very stable and generally reliable. ACWEECO did however make coil winders as the first three letters of the name represent. In 1948, there were still post-war shortages and it is quite likely that whatever suitable components were available were used from necessity.

PMM
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Old 9th Apr 2016, 10:11 am   #1343
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Default Re: AVO Multimeter survey

Thank you for your comprehensive response, you make an interesting point about the serial numbers, one be sure that the serial numbers were in continuos order and not in batches.

I can con confirm that both meters have block magnets.

The bobbin construction is more commonly found in meters made by other manufacturers which made me now wonder if that whole resistor section might have been outsourced.
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Old 9th Apr 2016, 11:49 am   #1344
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Richard,

I think it would be fair to say that the bobbin construction multiplier resistors are a standard form of instrument construction which dates from the earliest electrical instrumentation and were very widely used. They would have been in use for 20 - 30 years by the advent of the Avometer. It is a convenient technique for providing the resistances required as there was really no alternative to low temperature coefficient resistance wire at the time. By comparison, early carbon resistors were crude and had very poor consistency, stability and reliability.

The length of wire needed for the highest values was too great for bobbin winding which will have been why ACWEECO used slab winding for these multipliers until suitable high stability components could be bought from specialist manufacturers such as Welwyn, from the very late 1930s.

The Automatic Coil Winder and Electrical Equipment Company, ACWEECO, soon to change its name to AVO when your meters were made, took a pride in producing as many of the parts of the meters as they could within their own works so it is unlikely they would have bought in the resistance boards except if demand very greatly exceeded their internal capacity.

I would expect that ACWEECO's British an foreign patents would account for the lack of rival multimeters until the mid 1930s when, for example,Taylor, Simpson and Triplett started making what the Americans called VOMs. These manufacturers used component resistors from the start but they have proved less stable in the very long term, arguably longer than could reasonably be expected. It might be argued that design for a "reasonable" useful life, with some cost saving, is a responsible design choice.

PMM
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Old 9th Apr 2016, 7:18 pm   #1345
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Hi PMM

Thank you for the informations very detailed as to 13range. Unfortunately the only news as to Samar M.V.1 that I have refer to the work of a my friend in the RADAR maintenance army departments in Rome 10 years ago. Later I closed and are transferred outsider Rome (the museum originated in this area; MAXXI). Every technician was one Samar or an Avo7 although it is there were most modern measurers. I think that specific measurement of the radio set were prescribing measures whith the Avo7. I believe that Samar is much rare because normally, the military and civilian surplus in Italy it is detroyed for not making a parallel market. I saw three others exemplars by my friend and discovered what following the Avo numeration was (perhaps) in 1964/65/66. The inside of mine shows very great wiring, a huge magnet, Italian components (the screws are to European measure), the very peculiar bridge manufactured in Torino. The weight entire is superior at Avo7.

Ciao, Palmerino
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Old 12th Apr 2016, 3:19 pm   #1346
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Hi PMM

In effect there was another multimeter Samar. The Samar M.U.2, 20 kohm
(like Avo8 ?).

Palmerino
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Old 12th Apr 2016, 3:31 pm   #1347
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Internal of my Samar M.U.1 . Ciao Palmerino
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Old 16th Apr 2016, 7:25 pm   #1348
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Default Re: AVO Multimeter survey

PMM

You may already have this, I acquired it from a forum member at the recent Golborne meet.
Avo 8 Mk6 S/N 2471 M90095 although it is stamped "Mar 85" inside.
Sadly dead as a Dodo at the moment.
Regards
Martin
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Old 18th Apr 2016, 9:54 am   #1349
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PMM
Thank you for that, I had never thought about the reason for the slab construction and of course it makes perfect sense as a bobbins to accommodate the wire length of some of the resistors would be very large unless much finer wire was used.
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Old 19th Apr 2016, 8:57 pm   #1350
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Palermino,

Many thanks for taking the trouble to take these photographs and scans.

These are certainly very interesting meters and although they obviously copy many Avometer features, they seem to be very carefully constructed. Someone clearly went to a great deal of trouble to design and make these instruments so there must have been a very strong motivation. I have to wonder why it was not easier just to buy an actual Avometer as it would surely have been cheaper unless SAMAR made a considerable number of them. Perhaps the MU1 was designed in the late 1940s when there were still post-war shortages, but by the time of the Model 8/MU2, this was less of a problem although there could be long delivery delays until AVO opened their Dover factory around 1964.

I hope you will not mind if I have some more questions when I have had time to look more closely at the images which you posted.

PMM.
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Old 21st Apr 2016, 8:54 pm   #1351
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PMM

No problem, is a survey thrills! Hopes not boring for the other member of thread.

My Samar would have to be costructed more or less 1960 and have n.53665. Therefore not a big number who justifies such an undertaking expensive. Surely
the military bought the Avo7 that were probably costing less. I have two Avo7 of the same ward; n.54721-A-355, the second is not available. Maybe they were serving instruments built in Italy for not depending by abroad although this was
very expensive. How much does the Avo7-8 cost in England in 1955 and 1965 ?

Ciao. Palmerino
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Old 21st Apr 2016, 9:47 pm   #1352
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New (to me) is a non-working Air Ministry Type D, serial number D.46-1048.R.1949. It joins its fully working younger sibling, No. 342-D-9/1951 and its ailing older relative, No. D.2104-541.1941.

There seems to have been some variation in the format of the Type D serial numbers over the years, although the dating is pretty obvious.

The latter instrument, however, is a real odd-ball, being based on a Model 7 front panel and having a 1mA Model 7 movement but with the K=1 / K=2 switch. It doesn't work, and I have yet to fathom out how it should! I guess there must be an additional permanent shunt across the moving coil, plus a different value of swamp. Based on what PMM and others have said, I assume that in 1941 Avo were desperate to fulfill military contracts, and built Type Ds on whatever parts were available at the time.
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Old 24th Apr 2016, 10:38 pm   #1353
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I bought a Avominor type E n. E10060 1943 from Ebay last year. The instrument
had numerous resistor burned. The worse was the 20A and 2A range resistance
changed with other values. All the circuit was changed for as well measuring up to the AC. A Westinghouse bridge was imported and the K1-K2 commutations
changed in AC-DC, little professionally. As I wanted to restore the original electric circuit but I did not have the original diagram, I should have analizated the different combinations of contacts for many days until having to arrive to that consistent. I replaced the three wrapped resistences burned with these modern and many others. That of 2A range with costantan philum 0,8mm, with
many test and cuts. That of 20A range, the most difficult since I was not having philum adjusted diameter, I used five parallel segment of 0,8mm philum. The instrument is perfectly now working. I think that the 1000V range (2000V on K2) are very hazardous and I do not wonder of the resistance burned! Also 20A was a risk. For what were they using them? Did they be shipped on Lancaster bombers?

Regards. Palmerino
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Old 26th Apr 2016, 12:14 pm   #1354
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Avominor type E:

There I allege my electric diagram. If the original diagram has someone, it wold be helpful for a comparition. I have other two type E: n. E.16887.1944-
n. E.13779.1944. They have K1 and ohm/ampere only, original probably for security reasons. I use one of this for measuring batteries charges at home. To who asks me "why don't I use a digital multimeter?" (I use a Simpson 474 or a Avo/Megger M8037 for the most accurate measurements), I answer what
"this old veteran served honorably in RAF and now still work fine!".
The two photographs show the inside of the two different type E.

Best regards. Palmerino.
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Old 15th May 2016, 10:30 pm   #1355
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Despite my having declared "no more Avometers" in private and public, I just couldn't resist this dusty Air Ministry Model 7 for £2 at the NVCF this afternoon. Despite missing a few case screws, it is plastered with stickers suggesting a previous careful military owner and appears to be fully working and accurate!

Its serial number is 7944-16296.
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Old 24th May 2016, 7:58 am   #1356
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Quote:
Originally Posted by Palmerino View Post
Avominor type E:
Kia ora Paslmerimo,

I came across your post by accident and find it very interesting as I was not aware of the particular model AVO you have and have not seen it previously mentioned. You have made a real effort to restore it.

Regards from down under.

Trevor.
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Old 24th May 2016, 8:22 am   #1357
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Hello again Trevor,

There are quite a few posts elsewhere on the Forum concerning the AvoMinor Type E. I have a couple of these meters, both in non-working or scavenged condition on arrival and yet to be restored. The Type E was DC only.

Here's an example: https://www.vintage-radio.net/forum/...ad.php?t=87254

Phil
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Old 25th May 2016, 12:26 am   #1358
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Kia ora Phil

Nice to renew contact and and thanks for the interesting thread you have pointed out.

I have two AVO Miners and have again looked them out as they had become somewhat forgotten. Both are restored to good working order and have their original cases and instruction booklets.

The smaller DC version has an interesting little velvet lined case covered in a material much like that found on early cheap box Brownie cameras. The arrangement whereby voltage ranges can be doubled using the 6 mA plug socket is interesting and I wonder if this those who do not have the instructions are aware of this useful feature. Serial number. 4213-76 appears on the dial plate.

The Multiminor has no serial number on the dial plate, but 016165 appears rubber stamped within the metal enclosure.

Cheers, Trevor
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Old 25th May 2016, 2:43 pm   #1359
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My "Universal Avometer Model 7" number is: 1XXXX-A-550.

I bought it on Etsy after my digital meter went up the swanee. The shopkeeper was only selling the case as a 'vintage' item but the meter was a prop in some of the pictures. On enquiry, she sent it too for some extra postage!

Some number re-touching and polishing later and it looks wizard.
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Old 27th May 2016, 2:34 pm   #1360
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PMM

This is my AVO collection:
Best regards Palmerino.
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