AVO Multimeter survey

[pmmunro]

Congratulations on your acquisition Brandon and thanks for the information. The March 1956 serial number indicates one of the first of the Model 8 Mark IIs. I would expect that yours will have a space for a 250V (DC) range but no engraving and nothing connected for such a range.

As far as the book is concerned, that is the excu.., sorry, motivation behind my collection. Unfortunately the 37-hour a week part-time job that pays the money gets in the way a lot, together with other commitments.

I have a wide range of literature and archive material acquired for the project which will also be based on practical experience of Avometer repairs.

I also have a detailed service manual for the Model 8 part-written which I think might be of some interest.

For the present, send me a private message and I will return some background information.

PMM

[Brandon_R]

Thank you, and what a great service you've taken upon yourself to complete. It's understood such a task takes considerable time and energy. I'll private message you.

No, the 250V DC range is all there and complete.

[Leon Crampin]

It's the 500V DC range which is "missing" on the Mk 2 Avo 8s. There is a space for it though.

Leon.

[Brandon_R]

Thanks! wondered why it clicked there on the turn.

Question, the Holdtite aligator clips, made in London. Did these clips come with the Avometer or a seperate purchase? Seems most of the old clips I see with avos are Holdtite.

[pmmunro]

The Holdtite clips were standard supply with Avometers - in the familiar form from at least around 1950 and in an earlier form for some years before.

I think the piece of round bar brazed into the lead end of the clip was probably ACWEECO's (AVO's) specification, but perhaps someone knows better.

PMM

[Phil G4SPZ]

"This will be the last Avometer you buy, won't it Phil?" implored Claire. "Yes dear", I lied...

So my last (for now) new acquisition is a Model 40 Mk II, serial no. 2106-B-667-M. I don't think this had ever been opened up before, as the inspector's seal was intact, as was the sticky substance inside the bottom of the case. Unfortunately the instrument had to come apart because the DC current ranges weren't working, quickly cured by slight adjustment of the appropriate contact fingers. Inside, everything was pristine.

This meter is uncannily accurate despite being 45 years old - relatively young by AVO standards, as it was being made two months before Radio London closed down - and FSD agrees with my DVM to two decimal places.

[pmmunro]

Phil,

I know the experience; some Avometers are like that - they just have that impression of accuracy and dependability. It also shows that there is not normally any significant loss of magnetism.

The sticky substance is a grease put there to trap any small dust or debris which might otherwise reach the movement. I don't know what the original type of grease was. I use Petroleum jelly to replace it.

PMM

[Phil G4SPZ]

Thanks for that, Peter.

Another Model 7 Mk 1 squeezed through the letter box today, serial number 7545-21748. This one has a nice red disc on the pointer.

Phil

[Avonauris]

Hello, first post. Registered just to add my AVO 8 Mk 1½ mutant to this survey.

Finally located a pretty nice bakelite AVO 8, not as good and nice as many seen here.

This one is an old military surplus workhorse, calibrated in the FDF (Finnish defence forces) laboratory in 2008. It still has all calibration seals on it and seems to measure accurately what I have been tested so far. So no inside pictures for more precise ID.

Couldn't resist to show my other analoge meter (FET) in pictures. Just wondering should I get A Marconi rangemaster.

Serial on movement
Two oldtimers
Avo 8 mk1? backplate

[Paul Adams]

Originally Posted by Phil G4SPZ

"This will be the last Avometer you buy, won't it Phil?" implored Claire. "Yes dear", I lied...

Shame on you Phil, I am as bad though, with these two:

D.14537-544-1944 and 44690-A-1053.

No more as I am running out of space

Paul.

[Phil G4SPZ]

What do you mean, Paul, "running out of space"? You've got several other rooms, haven't you? I have to contain my Avo collection within a modest 10' by 10' shed...

I hope this is the right place for my question, which relates to the different styles of battery cover fitted to Universal Avometers with top access to the batteries. I have come across three cover types, and as these seem to be interchangeable (and probably get swapped around by previous owners) I wonder if specific types of battery cover were fitted to specific Models of Avometer, or whether the pattern simply changed over the years?

1) Bakelite with narrow slot and fixed 'overbridge' marked "PRODS" under which a pair of prods can be slid and retained
2) Bakelite with two slots and a rotating clip, to secure a pair of prods plus another probe of unknown type
3) Flat metal plate, finished to match the case

I'm tempted to think that cover type (1) is the early pattern, as I have an original Model 7 from 1947 with one like this. Type (2) could be a later pattern, as it is shown fitted to both Model 7 Mk II and Model 8 in images dated 1957 and 1960. Type (3) turns up on various Models.

Could it be that the flat metal battery cover was supplied as standard, and Bakelite battery covers were optional extras at additional cost?

[pmmunro]

Avonaurus,

Congratulations on your new acquisition - but I hope you've taken note of the serious risk of addiction as demonstrated by the two characters who sent the following posts. Also note that I'm not saying how many Avometers I've got. (I don't really know, but in Roman numerals I would need a 'C').

Paul,

I can see you're having to make a careful judgement on you life/Avo balance - not that you can't have both, despite what some people might think.

Phil,

The Bakelite cover with the slot and the 'Prods' legend is the oldest of the covers you describe and seems to have been introduced post Second World War. The version with broad slot and the rotating clip was used on Mark I and Mark II Model 8s which were supplied with two Holdtite clips, two insulated brass rod prods and a trigger type spring clip prod, the three prods being stored in the battery cover slots. I would have to check if contemporary Model 40 and Model 7s had the same accessories.

The trigger prod was not a great success; it was too clumsy and did not grip too well. It was replaced by "Prodclips" with their characteristic stepped conical shields. The Prodclips came in a vinyl pouch with a clear front and a dove grey back. For some reason, Avo decided to use a plain battery cover from then on rather than reverting to the earlier type for just the brass rod prods. Maybe they wanted to encourage the use of "Ever Ready" leather cases. In general, some of the Avometers in the best condition now are ones which always had a leather case to live in.

PMM

[Phil G4SPZ]

Peter,

Thank you very much; as ever, you have answered questions I had never even thought to pose! The trouble is, I have now got to search for a "trigger prod" to match the battery cover...

[Daventry 5XX]

Hi

I have just bought an AVO.

It is a model8 mk.v NATO version

Serial no.0548557 LE

December 1984

Regards

Alan

[Roger ZS1J]

Although I have some digital meters for accuracy, I still use an Avo Multiminor Mk V for analog measurements.

[Phil G4SPZ]

I've been wondering how many Avometers were built, and how many of them remain operational. For example, Land Rover proudly quote a statistic that "75% of all Land Rovers built since 1955 are still on the road" and it would be nice to know the same statistic for Avometers!

Presumably PMM has pieced together some production figures?

As a first guess, between the 1920s and 1990s we must be talking about several million units, with perhaps 30% of them still going. It sometimes feels like most of them are now in preservation at the hands of Forum members, but judging by the condition of some that I've rescued, there must have been a fairly high attrition rate once they got into the hands of electricians and Services personnel not to mention the number that were skipped when digital took over.

[noble kiwi]

Latest acquisitions, two model 9 Mk IV. Serial numbers 15467 & 15470, both 24/10/70. There are no stickers anywhere within and those on the outside are damaged so the at the first two figures are hard to read but I am fairly sure are correct.

Both are intermittent in operation and I have noted that silver migration problems relative to the rotary switches is common. First inspections have not disclosed anything and I would very much appreciate advice regarding what to look for and if the problem exists, how to fix it.

Also please, is there a copy of the service manual, or a circuit diagram, available anywhere on the net?

[Paul Adams]

Despite what I said earlier regarding no more, here’s a couple more that I must have bought unknowingly.

30204-C-155 and 403575-343

Now I have to find somewhere to put them, as all the other rooms are full.

Paul.

[pmmunro]

Paul,

So that's a Model 8 from January 1955 and a Model 40 from March 1943? In your excitement, you forgot to tell us.

PMM

[Refugee]

I have two MK9s. The one that has been cleaned with car wheel polish has the number 74890-94/8/72 and the other has no number shown at all. They are both in working order and are used at times when modern ones don't respond to quick changes in voltage.
They are both MK9 IV.