AVO Multimeter survey

[Superscope]

Hi Jonathan,

Thanks for the Numbers.

Your
1: sn 102024 869 will be a Model 8 and is most likely a Mk III judging by the Date (August 1969).

3: sn 8423 670 as you have said is a Test Set Multirange No 1 High Sensitivity
which was originally known as a Model 9sx (June 1960).

Regarding your no 4, from the description, this will be either a Model 8 Mk I or
an early Mk II. So it will fall somewhere on or between 1951 and 1956.

Sometimes, if your lucky, the original Serial Number was written in Pencil on the back
of the Scaleplate during Repair or replacement, but not always unfortunately.
Study every part of the movement. The Serial No could have been placed anywhere or nowhere.



Ian

[Sinewave]

Indeed for 1:, Avo never did a Mk8 anything.

[6.3volts]

Dave, thanks for your reply. Do you or anyone know if the absence of a serial number was normal for this era of Avo 8s?
The movement has red crackle painted magnets which I believe to be from a later date. I wonder if the scale plate is the original or came on this movement.
Jonathan.

[Sinewave]

If there's no serial on the plate, it's perhaps a replacement one which wasn't fitted by Avo themselves.

[pmmunro]

6.3V,

A photograph of your meter which lacks a serial number would probably help date it.

Red crackle paint on the magnets usually indicates a Model 8 Mark II (1956 to 1964). However, if it does have a replacement movement, the instrument made have been made at a different date.

PMM

[JoshWard]

I was recently given a new old stock Model 8 Mk V. Serial number 04450 8V/1/74
I was also given a Multiminor Mk IV and have looked all over it but can't find a serial number. Am I missing something obvious?

[pmmunro]

Josh,

There may not be a serial number on your Multiminor but some of the smaller Avo instruments of this age have the serial number stamped into the dial in small fine characters which are quite difficult to see. These numbers appear to be stamped into the paint on the scaleplate.

Congratulations on your Model 8 Mark 5. That really is a bit of good luck, or generosity by someone!

PMM

[Sinewave]

I've found one of my Multiminors hasn't a serial and the others have them stamped, but still difficult to see. I wonder if that means the Multiminor without the serial has a replacement movement?

[Superscope]

Survey Update.

Even though this Thread does go quiet occationally, a fair bit of work
is still going on behind the scenes.

Recent analysis

It is now seems certain, unless any information to the contary is forthcoming,
that before the introduction of the Model 7 in 1936, ACWEECO only used Two
numbering sequences for the Full Sized Meters (Excluding the Model 1).

The First was for the DC Range meters, thus, the Model 2 & 6 share the same Number Sequence.
We don't know how ACWEECO numbered their first Model 2 off the production line, as it is unlikely
to have been 0001.
It is more likely to have been 0100 or 1000, so unless we find earlier Numbers, it is assumed for now,
that Model 2's started at 1000.
Thus the complete Number Range was likely from 1000 until around 6800.
Obviously, we also don't know the final Model 6 Serial No, but 6745 is the last we do know about.
This implies, around 5800 DC Avometers in Total were made between 1927 and 1939, and most,
by a large margin being Model 2's.

The Second was for the Universal Range Meters, so Models 3, 4 & 5 all share the same
single sequence of numbers.
The Model 3 certainly started below 1000, as we have 13-919 recorded, so for now we will assume
the Model 3's started at 100.
The Universal Number Range is thus, likely to range from 100 until about 9000.
We don't know the number of the last ever Model 5, but we have 79-8686 recorded, so 8900 seems
plausible for the number of early Universals built.

Ian

[Superscope]

Following on from the last post,

We should now be able to estimate with better accuracy than before, the approximate Dates
the Model 2's were built.

The Following assumptions have been made:

Numbering started from 1000. If it was actually 0100, it won't make a hugh difference to the final calculations.

Production at Rochester Row didn't start until sometime between Apr-Oct, so
there wasn't a full years production in 1927, which one assumes is why we probably don't have a 1927 in our Database.

Key Milestones in Model 2 production are the move to Douglas Street. Known to be 1930.
Model 2 production believed to have ceased in 1936.
6052 is our highest Model 2 Serial Number.
Estimating the ebb and flow in production, with the start being slow and only part of the year, the peak in production being just before the release
of the Model 3, and then dropping dramatically after the introduction of first the Model 4 and then the Model 5.

Based on this, this is currently the best guess senario of Model 2 Production:


Serial Number range ---------------Year
1000 - 1150 ----------------------1927 Quarter Year Production? (Oct-Dec) Starting Serial 1000 ?
1151 - 1951 ----------------------1928
1952 - 2802 ----------------------1929
2803 - 3703 ----------------------1930
3704 - 4654 ----------------------1931
4655 - 5405 ----------------------1932 Model 3 Launch
5406 - 5756 ----------------------1933 Model 4 Launch (August)
5757 - 6032 ----------------------1934 Model 5 Launch (May)
6033 - 6158 ----------------------1935
6159 - 6239 ----------------------1936 Model 6 and Model 7 Launch

5230 Total Model 2's


Comments invited



Ian

[AndyGilham]

Ian
Its building up a nice picture, very useful information thank you. All this logging of products it proving very useful to us Meter Geeks!

Andy

[AndyGilham]

Morning Everyone.

A new instrument arrived in the post today.

Universal Avominor - Serial Number U.20052.84 (August 1934).
This is the earliest Model on my list of 120 serial numbers, and the first from 1934. Since the instrument was launched in 1934, I believe the serial numbering started at 20000, making this only the 52nd instrument off the line.

The instrument came in a nice wooden box and complete with leads

Andy

[SeanStevens]

I thought I had responded to this post - but I went through all posts I've ever made and could not find one........ my memory is starting to invent stuff!!


Model 8 MK II
113729-c-1060

Cheers

SEAN

[The Philpott]

Andy's Post no 2572:-

Certainly all the features i can see on that Avominor are early- probably there are two metal straps inside the rear (that do not appear on later meters)
One point of interest is the moulding- similar to certain Type E meters but lacking the ring upstands around the wander plug terminals- no doubt intended to stop the ends of the operators fingers touching the brass inserts.

Dave

[Pmark34]

hi all
not been on here for awhile , fantastic to see the recent posts, Great bit of work to be able to put some dates to the mk 2,3,4,5,6s and the launch of the 7.
I've another to add to the list which I don't think I've put on before, I believe it to be a MK 5 number 84-2866, saved it from becoming a lamp , Its not in the best of condition some of the old resistors need some tlc.

[The Philpott]

Post No.2575

Model 5 there, superficially quite good for it's age, well done.

Lamping has extended from common meters to rare ones on occasion lately,due to lack of research or lack of giving a damn!

Dave

[Superscope]

Andy's Post no 2572:

That's a nice find Andy!

However, there is a problem if you say the Avominor numbering may have started at 20,000.

We have U. 10775-34 logged in the Database which would not support that hypothesis.

That number comes from the list published on Page 112 Post 2227 of this Thread.


But, as I said previously, I'm no expert on Avo Minors.




Ian

[Superscope]

Post No.2573

Thanks for the number Sean.


Post No.2575

Thanks for the Photo's "Pmark34"
Always nice to see a surviving Pre War Model
Do you plan on restoring your Model 5 ?

Your Meter looks in pretty good shape, especially
the Scaleplate, which unusually, doesn't look like it is flaking paint.

Incidently, you did report the serial number back in
June 2017.



Ian

[The Philpott]

AVO Low resistance ohmmeter- switching assembly
(This is already on the survey, but i took some more pictures while refurbishing the faulty leaf switch stack which may be of interest)

One pair of contacts should close when pressing the high range button, two pairs should close when pressing the low range button. Erratic readings indicated this was no longer the case..

Mechanical tweaking of the leaves restored a good clearance when 'off' (to avoid flattening the cell) yet ensured firm contact when buttons pressed. A fine balance. I polished the (silver?) contacts as well, although blackening was not the actual problem. Certain parts of the spring leaves had to be polished (as well as the stamped out brass plate which holds the stack into the meter.)
A significant feature is that the clamping screw passes electricity from +ue on the cell to the leaf on the extreme right of the exploded picture. Polish everything to be sure, i told myself!
The insulators between the leaves appear to be cardboard.

It works now. Note the black tubular spacers- one to insulate the screw from unwanted contact with all but the last leaf, one to allow the low range button to close two pairs of contacts as simultaneously as possible. The bakelite moulding shows it's parentage- you can see the ghosts of the inserts placed in the mould to delete the multiple wander plug sockets of the DC Avominor.

Dave

[pmmunro]

Dave,

Thanks for taking the trouble to show us your fine work on the low-resistance Ohmmeter. As this is such a rare instrument, it's very fortunate that it came to you as you are able to appreciate its worth technically.

Once it's working to your satisfaction, will you be able to test its effectiveness? Low resistance is notoriously difficult to measure due to the influence of every contact point in the test circuit, not to mention within the test meter.

It would be interesting to know what its intended principal application was. At the time Megger, (not then part of the same company), hand cranked insulation and continuity testers were widely avaliable and would have been used to check low resistances.

Modern insulation/continuity testers seem to be quite good at measuring down to a few parts per hundred and readings which reflect this are regularly enetered on electrical test certificates.

The specification for a typical modern instrument (Megger MIT 310 series) is;

Characteristics - Continuity ranges

Measuring range: 0,01 Ω - 100 Ω
(0 -50 Ω on analogue scale)
Open circuit voltage: 5 V ±1 V
Short circuit current: 205 mA +10 mA -5 mA
Accuracy (at 20° C)
MIT300, 310, 320, 330: ±3% ±2 digits

Do you have the specification for the Low Resistance Ohmmeter?

The subject of low resistance measurement seems to have been of some interest to ACWEECO at the time as the attached advertisement shows. This show different approachs to low resistance measurement. The bonding meter is described as using the crossed coil technique and a 10Ah nickel iron accumulator - presumably similar in principle to a Megger and the "Milliohmmeter" used "An external 2V accumulator". The six terminals on top of the Milliohmmeter would suggest that it used the 4-wire technique.

PMM