AVO Multimeter survey

[wave solder]

A few more Avometers acquired,

Avo 12D and what I presume is the serial number:- GJR 12D R84

These two looking sorry for themselves but nearly functional:-
DA117 S/N 0040638 EB
DA116 S/N 02699 116/11/79.

[Donkey1]

G'day chaps!

My first post, and just to let you know that I have acquired what I believe is an Avo 8 MkV.

A British Telecom MMR.14.C with the serial number 1116 M90707 8/6 14C/3 (with what I presume is a manufacture date of) 8/86.

Resplendent in it's tan coloured hard leather case, it looks barely used.

Dave

Moderator note; further questions on this meter have been moved to a new thread here.

[pmmunro]

Dave,

Does your meter have 3000V (AC & DC) sockets at the top corners of the front panel? If it does, it is a Model 8 Mk V, if not it will be a Mark 6.

Functionally these are very similar but the Mark 6 has only rigid printed circuit boards whereas the Mark V has flexible printed wiring to interconnect the main boards. This change brought about a change in the range switch layout so that the voltage ranges are both on the inside radius of the switches in the Mark 6.

PMM

[davidgem1406]

Hi,

Just bought an AVO Model 8 MK V in pristine condition with original leads and leather case. So far seems to be all fully working The case is in good overall condition but a little worn.

This AVO has no serial number or year marked anywhere to be found.

Dave

[davidgem1406]

Another to add in, just arrived with me.
Model 8 and I think a MKII Serial No. 53043-C-1156 I believe that makes it a 1956 model? I have added a picture.

It is in fairly good condition but needs some attention to the engraving and a bit of a clean up.
Not tested it out as yet but opened it up and it has no problems inside everything is looking good. The movement is free and the cutout is in good order. Battery compartment is clean and corrosion free.
Range switches click round positively and smoothly.

Internally it looks just like the MKI I rebuilt a short while ago.

I fully expect this one to work OK, we will see!

Dave

[datadiffusion]

Just been getting my old electronics kit out of storage today, where its been for, pretty much, 7 years. I was just having a look at my Model 8 Mk VII Avometer, and trying to see about the batteries online (by some kind of luck, I forgot to remove them before storage and not only have they NOT leaked, the meter works pretty much prefectly, although they are obviously a bit flat) when I found out they stopped making them in 2008. Not sure why I'm so surprised, but then I've been out of the loop since 2007 - retraining for 2 years and working in a totally different field now!

So, sounds like this is one of the few with a solid PCB? Again, something I didn't realise, I just assumed all 1970s models onwards would be like this. Not that I ever opened up the case, as its always worked well, and thankfully never been dropped...!

Serial no. is M7541801007 0992 - does this mean its from September 1992? It doesn't look it, esp. since I only bought it used in 2005. Must have had a very quiet life before I got hold of it! Be interesting to hear what people think of this last of the line model, you don't get that many results from searching for it, but I did see a company still hiring them out by the week for £££!

keep up the good work,

Stuart

[pmmunro]

Dave,

Your meter is a Model 8 Mark II and you have read the date of manufacture correctly. This is an early Mark II which is why it does not have a 500V (AC) range, although there is a space for one on the switch.

Internally, there is a change to the movement magnet. The original Model 8 used alnico block magnets which are not painted. In the Mark II the front to back dimension of the magnets is reduced to 5/8" and they are painted with red crackle paint.

The service manual recommends that the engravings are filled with cellulose paint - car touch-up paint. This does not have to be exactly confined to the engraving but it is important not to allow any onto the "leather-grain" finish of the front panel or the straight knurling of the knobs. The paint should be allowed to dry for a few hours. It is then rubbed with a cloth dampened in methylated spirit which removes the excess and leaves the engraving looking like new.

Before starting the refilling, you may want to scrape out any loose paint remaining in the engravings but care is needed not to scratch the surrounding surface.

If the front panel needs to be cleaned, an few spots of hand dish washing detergent and a little warm water works well with a stiff toothbrush (Avometers are worth a new one although they might tolerate an old one). The foam can be removed with a damp sponge, but takes some time. If removal of the movement from the front panel can be justified and you are confident about resetting the cut-out adjustment, the panel can be cleaned with gently running water, taking care to keep the inside components, especially the transformer, dry.

The final finishing touch is to "dress" the front panel with a few drops of thin oil (eg 3 in 1) applied with a cotton wool pad or similar.

If you have been following other threads, you will know that with the meter out of its case, the Bakelite plates on which the ohms pots. are mounted are easily broken by any side pressure on the long hexagonal pointed studs which connect to the battery compartment fingers.


PMM

[pmmunro]

Stuart,

It was around the time your meter was made in September 1992 that the design changed from the Mark 6 to the Mark 7. The internal construction is very similar and differs from the Mark V (1972 - c. 1980) in dispensing with the printed flexible wiring, which is very delicate.

There has been a lot of adverse criticism of the Mark V and the two principle weaknesses seem to be the flexible printed wiring and glass loaded nylon pivot bridges in the movement. I have seen some terribly abused Mark Vs suggesting that, from the 1970s, many users took (even) less care of these meters than in past times.

Many people much prefer the earlier Avometers and find the Mark V inferior. Against this it has to be considered that the later marks were designed to meet stringent NATO specifications. In my experience, good ones are accurate and reliable although the resistance range adjustments can be temperamental. There have been fewer comments about the Marks 6 & 7, possibly because there are fewer of them used by private owners.

By the 1980s and 1990s far fewer analogue multimeters were being used and the price of Avometers was rising steadily. Both analogue and digital meters have their uses but ultimately it would have been difficult to justify the price of around £900 for an Avometer. I would suggest that many sales were only to meet the specification in older Services and aerospace service manuals that readings should be taken with an Model 8 Avometer.

Comparisons have also been made with some excellent European analogue multimeters which have more advanced cut-out arrangements and it could be that the Avometer design was to some extent a victim of its success as change was unwelcome to dedicated users. There is also the question of how committed the company owners might have been to development costs.

PMM

[davidgem1406]

Hello PPM,

Thanks for all the information.
When I rebuilt the MKI I used wax to refill the engraving, much easier than using paint. Also the zero pot brackets were both cracked and I repaired them OK.
I just need to clean up the front and terminals a bit so I wont be taking this one apart. Still have to check all the ranges though.
I learned a good deal from doing the last one thanks to all your information and advice.
There are now 3 sitting on my shelf a MKI, MKII and a MKV. The MKV is the one I use.

Regards Dave

[Phil G4SPZ]

I hope Peter will permit me to suggest some alternative techniques for cleaning up Avometers which I have found simple and effective.

Originally Posted by pmmunro

The service manual recommends that the engravings are filled with cellulose paint - car touch-up paint.

White wax crayon is quick and easy and gives excellent results, particularly on Model 7s. On Model 8s I prefer to use a sharp Chinagraph pencil.

Originally Posted by pmmunro

Before starting the refilling, you may want to scrape out any loose paint remaining in the engravings but care is needed not to scratch the surrounding surface.

A sewing needle is ideal for this task, and with care can also be used to pick paint spots etc. off the front panel.

Originally Posted by pmmunro

If the front panel needs to be cleaned, a few spots of hand dish washing detergent and a little warm water works well with a stiff toothbrush

I have found that unperfumed baby wipes are quicker, less messy and more effective. I have cleaned many Avometers that have also been splashed with paint, varnish and other substances, which had set hard but all eventually responded to solvents of varying aggressiveness, such as meths, lighter fuel and IPA. Fortunately the patterned Bakelite front panels are very durable and resist all solvents tried to date; I haven't had to resort to acetone or cellulose thinners yet, though.

Originally Posted by pmmunro

The final finishing touch is to "dress" the front panel with a few drops of thin oil (eg 3 in 1) applied with a cotton wool pad or similar.

Silicone spray sold as 'dashboard shine' also works extremely well and the resultant cleaned surface doesn't attract dust; spray into a small container, then apply the liquid with a cut-down 1/2" bristle paint brush, and polish off with a clean cloth.

[threeseven]

Have been lucky enough to just acquire an Avo 9 MKII in as new condition with case and leads !
S/no 12610.1267, which I assume to be a December '67 unit ?
I am so chuffed to get a 9, they seem to be so scarce, and in this condition a real gem !

Also acquired a nice Multiminor MK 5, s/no 00123. Has a Nato part # on the upper left of the top plate.

Also, I have a little tip for cleaning dust from the top panels of Avo 7, 8 etc. Blutak !!
Just press a ball of it into the panel and it takes out all but the stubborn stuff.
To re-fill the white markings I use a paint pen, wiping away the surplus with a business card.

[Valvewhiz1]

My Dad's Avo8 Mark 2 No. 140463-C-562, I didn't realise it was that old!! I used to get told off if I touched it!!

Picked up an Admiralty Pattern 47A yesterday No. 8433-642 making it nearly 70 years old, no battery though, but in a nice wooden case..

[pmmunro]

Phil,

I hadn't thought to use impregnated wipes to clean Avometers but I have found them very effective on other things so I will probably give that a go. A refinement on the sewing needle engraving pick might be to use a pin chuck to hold it which would give a better grip.

The silicon spray also sounds a good tip - I don't suppose it was available in the 1950s when the manual was written. Silicon spray can have devastating effects on paint spraying but I wouldn't think that's too relevant here. I've had good results with 3 in 1 oil (and I like the smell) but I've always been surprised that it doesn't hold dust.

Wax filling has a long tradition for engraving and shouldn't harden. It's probably a matter of personal preference and what is to hand.

Congratulations threeseven - now you will need to find a Model 9 Mark IV with no cracks in the case - that is a challenge.

Valvewhiz 1 - thanks for the numbers. I obviously don't need to tell you to look after them carefully, you seem pleasantly excited. Avometers have that effect.

PMM.

[threeseven]

Originally Posted by pmmunro

Phil,


Congratulations threeseven - now you will need to find a Model 9 Mark IV with no cracks in the case - that is a challenge.

.

Indeed it will be I've never even seen one !
Thing is, I never intended to have an Avo collection, it's crept up on me !
I'm even collecting shunts, transformers etc now.

[Alistair D]

The way I usually polish the front of Avos is a bit different and does not need any polish. I have a couple of very soft felt pads for my Dremel type hand tool. The pads are so soft that there is no chance of wearing away the bakelite. Turn down the speed of the tool to a few hundred RPM and lightly press the pad against the surface. The results are especially noticeable on the range knobs and their escutcheons.
Rather than using a needle for filling in the paint markings I use a cocktail stick stick. That way there is no chance of adding extra scratches.

Al

[noble kiwi]

Originally Posted by threeseven

Indeed it will be I've never even seen one !
Thing is, I never intended to have an Avo collection, it's crept up on me !
I'm even collecting shunts, transformers etc now.

I have two Model 9 Mk IV, both with perfect cases, Serial No’s. 15467. & 15470. Incidentally I have also collected a few accessories.

Trevor.

[threeseven]

Thats just greedy, so sell me one

[on2itmaclennan]

Hello,

I recently picked up two Avo 9 mk 2 meters, serial numbers below:

6453.866
4129.1265

Hope that helps.

Thanks,
Andrew

[Paul Adams]

9SX, Serial Number: 8Q39-15-964.

Paul.

[Valvewhiz1]

Hi Again,

I also have an Avominor s/n U.90582-646 and an Avominor 2 s/n 1724-254.

The Avominor is in its original box with instructions..

AJH