Is there an AVO Model 9 Mk 4?

[Sara-4711]

Hello,
Is there a AVOmeter model 9 MK4?
If yes, a) what is the difference between AVO8 Mk4 and AVO9 Mk4?
b) why is AVO9 heavier than AVO8?
Greatful for any comments.
BR
/Lars G

[Refugee]

There is such a thing as a model 9 IV (4 in roman) in my workshop and another in my static display in the lounge.

The answer Sara-4711 wanted, yes.

[pmmunro]

The Avometer Model 9 was introduced in September 1964 and was an "international" version of the Model 8. The Model 8 Mark III came out two months earlier in July. For some reason, no more logical than their usual practice, AVO chose to call the first Model 9 a Mark II.

The Model 9 has pictographic symbols for the switch and terminal markings and is scaled in a 1 - 3 - 10 sequence: the Model 8 scales were in the sequence 1 - 2.5 - 10 and marked in English language words or initials.

Compared to the previous mark, the Model 8 Mark III had a more compact magnet assembly, thermistor compensation, more sensitive 2.5V, 10V & 25V alternating voltage ranges and a fuse for the ohms ranges. There never was a Model 9 Mark III.

In order to reduce the cost of production, both meters were redesigned internally to become the Mark IV which had a thermoplastic back case instead of the previous phenolic resin case (Bakelite).

Both the Model 8 Mark III and the Model 9 Mark II are stated to weigh 2.95 kg in the 1967 short-from catalogue, which is the same as the Model 8 Mark II. The same weights are given in the 1970 short-form catalogue for the Mark IV versions. The screened panclimatic Models 8SX and Model 9SX are considerably heavier. By 1970, both screened panclimatic models were replaced by the Test Set Multi-range No 1 to Ministry of Defense specification DEF-155 which had the scale sequence of the Model 9 but English language markings.

PMM

[Sara-4711]

As usually, comprehensive answers from Pmmunro and Refugee!
Thanks vey much.
/Lars G

[M0XNA Neil]

PMM
My AVO 9SX has all English scripts like the TS1 and a 'crows foot' symbol on the scale plate, but no scale fit number.

Neil

[pmmunro]

Neil,

Can you give us some pictures please? It is possible that your 9SX is a hybrid with a case from another meter, but photographs will help in determining this.

The "crow's foot", officially a "Broad Arrow" or "Feon" , tells us it once belonged to Her Majesty. The lack of a scale characteristic number would probably make the movement earlier than AVO's move to Dover since it was about this time that the system was adopted for these meters. I think you said it does not have a serial number on the scale plate; some military meters have the serial number on the lower left rather the right as usual. Otherwise the lack of a serial number could either be because the movement is a replacement unit or that it was made after the self-adhesive label serial number system was introducted. If a replacement movement has been fitted, the serial number should have been written in, but this was not always done.

PMM.

[M0XNA Neil]

PMM
The AVO9 SX has a serial number of 8673 - 15 - 765 and has the following written in the lower centre of the scale plate:

Multimeter type 12889 /l\ 5QP/17447.

It is accurate, in excellent condition and the vertical pointer balance is within 1% of scale. I have attached a photo.

Neil

[pmmunro]

Neil,

The Multimeter type 12889 5QP/17447 is described in A.P. 4343J, Vol. 1, Sect. 2 according to information in the IEE Archives; I don't think there is any question that this is what your meter is. It has the simplified scaleplate markings of this military meter and the voltage/current scale is on the largest radius where the resistance scale normally is. The 12889 arrangement is more logical as is improves the accuracy slightly on what are the most used scales where the greatest accuracy is needed, or at least expected.

The 12889 seems to be very similar to the TEST SET Multirange High Sensitivity No 1. It could be that they correspond to the Model 8 Marks II and III, with the differences already mentioned. My Test Set No. 1 is dated 1970 which would support this very slim evidence. When I have time I must check the serial numbers of any in the Avometer survey.

I can't explain why your meter has a "9SX" button above the cut-out as this is neither a Model 8 nor a Model 9, but something of a cross between the two but without the most sensitive alternating current ranges. During the Second World War, ACWEECO seemed to use whatever front panels were to hand for Models 40, AM Type D and Admiralty Pattern 47A and 48A. However, by 1965 there was no need for this.

I don't have a 12889 to compare to yours so I can't say what type button would normally be fitted; does any one else?

I think the leather case may also be one which this meter has acquired in later life. Military cases were usually black leather, black synthetic board or olive green drab vinyl.

PMM

[Refugee]

I have got a picture of one of my two.
It has the serial number on the dial :- 7890-94/8/72
I would be prepared to say that it is a 1972 vintage.
It has been cleaned using my semi wet method using car wheel cleaner and came up very well. My other one is busy doing workshop duties.
Any idea how to trim up that Araldite that has been used to repair the glass?

[M0XNA Neil]

PMM
I was surprised to see the dB scale on the innermost arc of the scaleplate as I thought the MoD didn't use it. Having looked at the inside of this AVO, the encapsulated AC transformer is marked as 'MOD.9SX PT No. 20252 - LX.

Neil

[Paul Adams]

I know I said I wasn’t going to buy any more, but couldn’t resist this.

Here’s a picture of my 9SX with it’s original military style black case.
Serial Number: 8Q39-15-964.

There is another number engraved above the scale, on the bakelite which is: 6625-99-949-1853, just to confuse everyone.

Paul.

[pmmunro]

Paul,

If this is a Model 9 it's not as we know them. Until this thread, I believed that, by definition a Model 9 had pictograph symbols instead of words or initials for the English language. I'm still fairly sure this is the case, but now we have two military meters with a Model 9SX button on the front panel, one from 1964 and one from 1965.

Does yours have the number 12889 anywhere?

The Nato number 6625-99-949-1853, seems to have been used for the AVO Test Set High Resistance No 1, which is very similar; it may even be just a change of designation with no change in technical details.

At present, th best explanation I can suggest, in default of any attributable evidence, is that 12889 is too big for a designation button so it was decided that Model 9SX was the next nearest.

Information from the instruction plate on the back of the case might help.

PMM

[Paul Adams]

PMM,
Sorry for the confusion, that one looks like a bit of a hybrid, as there is no instruction plate on the rear, and I cannot see the 12889 number anywhere.

I also thought that the model 9 had the graphical symbols too, as my other model 9’s are clearly marked with these symbols.

Just to add more confusion, I have an 8X with a chrome screw type button replacing the normal reverse MC button, what was the inclusion of this for.

Paul.

[pmmunro]

I have now had a chance to check my original reference to the Multimeter Type 12889 which states that "This testmeter is similar to the Multimeter, Type 1 but has an improved scale and incorporates a.c. and d.c. ranges. The instrument is panclimatic and has a sensitivity of 20,000 ohms per volt .... The ranges are in the 1 - 3 -10 sequence.
The Multimeter Type 1 is an apparently standard Model 8 Mark II.

There is a small photograph which is clear enough to show the voltage and current scales on the outer arc, the resistance scale below and above the mirror and a decibel scale below the mirror.

The Model identification is not entirely clear but does appear to be marked "9SX".

I have no direct evidence, but I am now inclined to think that there was a Model 9 Mark I and this is it. There were probably never any other variants than the 9SX and I don't think it was ever offered on the civilian market.

As ministries are obliged to do, they have to have their own name for everything and so they designated the meter "Type 12889". As far as AVO were concerned, this would have been different to any Model 8 and so perhaps, by design or usage, it came to be known as a Model 9. Having seen the advantages of the 1 - 3 -10 range sequence, especially for export markets, they could have decided to offer a standard version for the commercial market, complete with pictographic symbols - the Model 9 Mark II.

Please note that this possible explanation is all speculation; any hard evidence would be welcome.

If this is correct, the 9SX developed into the "Test Set High Sensitivity No1" by losing the decibel scale and adopting modifications similar to the contemporary Model 8 Mark III, i.e. the fuse in the resistance ranges and thermistor movement compensation.


Paul,

I haven't had the chance to check out the 'Rev MC' button with the metal surround; it seems to have been used selectively on military meters. Does it latch?

PMM

[Paul Adams]

PMM,
The metal surrounded 'Rev MC' button dosn't seem to latch on the one I have it just acts like a push button, but the rubber seal around it has perished and has gone hard.

Will have to open up the meter, to see if it is supposed to latch.

Paul.

[Paul Adams]

PMM,
I cannot find any indication that this switch is of the latching type, it just looks to be momentary, it took me ages to get the screws out of the case. (had to drill a couple out)

Is it me or is everyone addicted to that lovely smell when you open up an old AVO.

Paul.

[threeseven]

Can't say I'm addicted but I also do enjoy that smell !

[M0XNA Neil]

PMM,

Here is an image of the back of my AVO 9 SX which indicates that it was manufactured at the London manufacturing site and was a test set No 1, panclimatic. The meter is a 'hardened' AVO 8 Mk 2 with no resistance range fuses and the simplified MOD 0-100, 0-30 scaleplate.

Neil

[pmmunro]

Some months back we had this discussion about the Avometer Model 9SX during which I learned that I had been wrong in thinking that the Model 9 Mark II was the first version.

While looking up information for another thread, I have just discovered a reference to the Model 9SX in a Avo commercial price list dated may 1962. It is listed under "Special Purpose Instruments" at a price of £29-0-0, the same as the contemporary Model 8SX. So I was wrong about it not having been available on the commercial market too - and I've had that price list for about 50 years! Still, I have never seen it advertised except for that price list entry.

Possibly it was sold to civilian contractors who used it on Air Ministry work to comply with specifications. It is also possible that it could be supplied as part of the equipment which went with the aircraft and was bought in by the manufacturer for onward supply.

PMM.