AVO Multimeter survey

[scotty48]

Hi I have a AVO 8 serial number: 42617-C-1255

[JohanBee]

Thanks for all information of my AVO-meter Model 21S.
I now understand it is a quite rare export Swedish version of the 6A extended current version of Model 20 and I’ll take good care of it. Also the extended scales with multiples of 3X & 12X are also more convinient for servicing, but lacking the full scale 6X-markings?, you have to multply or divide in your head!

It’s not any active electronics in it, so passive and the batteries 1,5V AA & 15V are only used for the Ohm ranges.
I have looked for the AVO serial No. but can’t find any. Maybe it is hidden inside, so i have to part it...but have not done.

It and other AVO products was imported by the swedish company SRA (Svenska Radioaktiebolaget), a large very serious radio/communication company (they even manufactured tubes/valves under the brand SER & Ericsson) , founded in 1919 by five other large swedish companies to do research and designs of the then new radio electronics industry. In the 60’s it was mainly owned by Ericsson and was later merged to Ericsson.

I have lifted the back side plate and it vas very difficult as it was like glued with some sticky resin on all four sides. I can see some prying marks in the two lower corners, probably from the service/inspection guys when pryed open for inserting batteries by testing.

I did not put any batteries in it (fear of leaking) as I better use my digital meters for Ohmic measurements. But I’ll use it for voltage measurments in tube radios, as the stated values often is recorded with an analogue 20.000 Ohm/V meter.

I see the last inspection was the 29th October 1984 on the label on top. That was not recorded on the units slip. The next inspection should then havebeen done be in October 1985, but it was probably decomissioned and just left in storage.

I bought it in the beginning of the 90’s from a (now closed) Navy surplus shop and have not used, just stored it.
I now asked about it when I joined this forum and found out there was so much expertise and knowledge collected here.

I will use it very sparsly and all time keep it in the original case and not move it around on my service bench, to keep it in the good condition as it is.

I used a couple of sucktion cups from a bathroom utility to pull off the lid, instead of prying. Can recommend that when you can’t grip a smoth furface. I was afraid there was a forgotten battery that have leaked (Duracell?), but the sticky and partally dried stuff seemed to be like solder flux and was disolved and cleaned away with isoprophylic alkohol.

I have attached some more photos of it including diagram and if someone wants better resolution for dokumentation, you can PM me and I’ll send by eMail.

Now preparing to go south a couple of month to escape the worst winter weather here in Sweden, so I’ll have no access to the meter for some time for new photos.

[AndyGilham]

A new Avometer Model D for the Megger collection.
This is an interesting one.

Original serial number is 1269-1140 (November 1940). As detailed on scaleplate and in pencil on rear of the movement. The rear of movement also states 17-06-49 and 1949 is also printed on the scaleplate next to the serial number.

This implies the scale was replaced in 1949? but still lined with the original serial number.

Top center of the scale has the A<Crown>M for Air Ministry.
Bottom center of scaleplate has Air Ministry Phenon and under that Ref.10S/10610 and then under that LGC/R/12/67
Bottom left of scaleplate R.A.F.27

Front panel is a Model 40 moulded panel

Rear instruction plate is full length (rather than Model 5 style), but reads 10A/10610. So this raises some questions, when did the specification from 10A/10610 to 10S/10610 change over? Clearly there were 10A/10610 plates manufactured for Model 40 based instruments.

Andy

[Barnmead]

The initial numbers and letters indicate the class or potential use of the item:
10A Miscellaneous Radio (Wireless) Equipment
10S Radio (Wireless and Radar) Test Equipment
The test meter type D was a versatile instrument so could be stored and referenced under either category.
But then you might wonder why it could not have been given a 5Q number:
5Q Ammeters, Micro-ammeters, Milli-ammeters, Voltmeters and Milli-voltmeters

Maybe the change came after the introduction of Radar or were binstruments with both 10A and 10S made simultaneously?

[AndyGilham]

I was aware of those categories, but had assumed that 10A was replaced by the 10S standard.... With the increase in radio/radar....etc.
It's quite possible both were active over the same period of time..... Hence my one being a combination!

[pmmunro]

I have a 10A/10610 version which is definitely based on a 36-range Universal meter and has fuse protection. I obtained this one from Germany, so it probably had an interesting history.

The Avometer Model D shown in AP1196E is listed as 10S/10610 but the illustration shows a meter whose serial number appears to be D179-119 1939. It is on a Model 40 front panel. The battery cover is on top and the case has wrinkle finish paint indicating an aluminium back-case.

It would be very helpful if any sales records or Air Ministry specifications still existed from this time because there seems to have been some "mixing and matching" to meet production demands.

The information from Barmead is interesting. The ranges and sensitivity of the Model 'D' have always suggested to me that the instrument was intended for aircraft or motor vehicle electrical systems. The Model 7 would appear to be more suited to radio and radar work. Is it possible that there wasn't a suitable category for an aircraft/motor vehicle test meter and so it was given a 10A or 10S prefix? AP1196E describes various instruments but does not state their intended area of use.

PMM.

[AndyGilham]

Another instrument has arrived...... plus an interesting donation....

I have received an Admiralty Pattern 47A with 'well worn' carry case.
Serial number 16860-944

The instrument is in pretty good condition and a nice additon to the collection. An interesting observation is the scale lining. the '480V' text looks to be smaller than the other text. I get the feeling the person lining the scale went a little over zealous with their writing and run out of space....
Once again....the 'J' also appears..

The second instrument, albeit not a Avometer, is in fact an Avo Radiac meter. Known as the RSM (Radiac Survey Meter) Mk 4.
No serial number on the small display, but marked 1545 in the rear.
Just thought i would add it as an interesting design....

[Barnmead]

Further to the 10A/ 10S/ puzzle I have wondered if the other Air Ministry test meter models (C,E,F, and H) were also made with the 10A/ reference. You will see what I have discovered here: http://www.richardsradios.co.uk/militaryavos.html that the type F also had a a 5QP/ reference.

I have found that my SEI version of the model D has a 3mA rather than the 2.5 mA sensitivity of the AVO design and that it was used for radar work. see the attached pictures.

[Sinewave]

Three for me to add tonight.

Model 12 - Serial: No. 4293-4-72. Supplied in the lovely case with accessories and operating instructions.

Heavy Duty Avometer - Serial: No. 5209-855. British Railways Signal Eng. Dept. London Midland Region. With the British Railways case too.

And I got lucky here, I found another 20 range model 3. Serial: No. 92-392. It is absolutely spotless, even the rear instruction plate is completely legible and immaculate.

[Barnmead]

More on the 10A/ 10S/ puzzle. A recent item for auction was described as follows:
Testmeter type 'E' Ex Air Ministry Reference Number 10A/10613 Serial Number E19406 Date marked 1944 on scale plate.

Although the instrument does not appear to have 10A/10613 on its case or instruction plate, the part numbers for the fuse, clips and prods have 10A/ references rather than the 10S/ ones in AP 10955H Vol1 Section2 Nov1943. Attached is picture of instruction plate.

[Sinewave]

Barnmead, did you see my post #2353 with the Type E I found at Hendon's RAF Museum?

[Barnmead]

Sinewave
Yes I did, although you can only see the front, the leather can is clearly has a 10S/ reference.

Perhaps Andy can say how this one fits in with all the others he has collated?

So far it looks as if 10A/ and 10S/ were going together for a while. Could it be that there was some minor difference in the specification or merely that some of those at the Air ministry that purchased new batches used different versions of the AP documents when placing the orders.

[The Philpott]

Just seen a Universal Avominor for sale with the instruction plate marked with
AD PATT 13301. I was not previously aware that the Admiralty had used batch/es of these meters. It has the early type facia, predictably quite tired looking and appears to be cracked. I wonder if the insides have more environmental protection than the standard article (probably not)

Dave

[pmmunro]

Dave,

That's a meter variant I hadn't been aware of either. It would be interesting to know, as you suggest, if it might be treated to be more resistant to a marine environment. Certainly there seem to be signs that the 47A/48A meters are.

PMM

[Barnmead]

I was given nice clean one of these last year see here http://www.richardsradios.co.uk/avominor.html
but have not removed the inner cover so cannot say if it is in anyway special.

[The Philpott]

Well.. the AD PATT meter sold, i just hope it's not been bought up cheaply for re-purposing.
(In any case at least there is one similar in captivity for research.)
Dave

[Superscope]

Wishing everybody on the Forum a very Merry Christmas
and a Happy New Year.

Please find attached the Multimeter Survey 4th Edition.

Special thanks to PMM for proof reading my Draft and offering a few comments
and corrections.

Hope you find this interesting and informative.
A lot has been added since the last Edition.

Once again, comments and suggestions, good or bad are welcome.


Ian

[Barnmead]

Epic piece of work, well done. Thank you, I’m sure others will agree.

[The Philpott]

Absolutely Ian, it's top banana. If there's any other photos or details you need i will contribute if i'm able to.

Dave

[ex 2 Base]

Brilliant, what an interesting and informative piece of writing,well done. Ted