AVO Multimeter survey

[Phil G4SPZ]

Bonding testers were probably produced by several manufacturers in response to demand and contracts from the Air Ministry. I recently restored a “Record” bond tester which works on the same crossed coil movement principle, has a FSD of 0.1 ohm and can be read down to 1 milliohm. The scaleplate refers to A.P. 19744 and carries the WD ‘phaeon’.

Instruments of this type don’t seem to survive very well due to leakage of electrolyte from the wet NiFe cell, and are rare as a result. Mine had suffered severe internal corrosion and only just escaped recycling!

[Superscope]

Excellent Work Dave,

Not only have you got a very Rare Avo Meter, but one
in virtually as New Condition now.
I wish my Solder Joints were as neat as that!


Likewise, excellent work on the Bond Tester Phil.
That was also a nicely written up account, which I
hadn't seen before.

"A most excellent and bodacious item!"

I haven't decided yet which of you Two Guys are the most
Artistic with your descriptive use of the English Language.

Always a Joy to read.


Thanks




Ian

[pmmunro]

Phil,

I missed your earlier thread about the Record Bonding Tester and as that thread is now closed, please accept my belated thanks and congratulations on your research, write-up and restoration work.

It's possible, that like the Air Ministery Testmeter Type 'D', several manufacturers supplied instruments to the same specification. If that was the case, perhaps the ACWEECO bonding tester was supplied as an alternative to the Evershed & Vignoles and record testers.

Perhaps one of the fascinations of these old instruments is the ingenious techniques their designers used to overcome the challenges which today can use electronics to meet and exceed the challenges.

(Possibly this tangential discussion aside form the main Avometer theme should be a separate thread; it does however relate to measuring Avometer shunt components)?

PMM

[Phil G4SPZ]

Originally Posted by Superscope

...I haven't decided yet which of you Two Guys are the most Artistic with your descriptive use of the English Language...

Ian,

I barely merit your most fulsome and effusive praise, kind Sir, yet it is humbly accepted and greatly appreciated.

Innit, Dave?!

[The Philpott]

Avo Low resistance Ohmmeter

Phil, i agree, it's appreciated like a Guinea found with a metal detector on a rainy day!

Ian, thanks, my solder joints aren't always as good and i generally get a loupe on them before i pass them as bonded rather than a bead sitting on top! These ones went quite well.

Peter, thanks, i appreciate it. I don't have spec for the instrument.. unfortunately when i quoted resistances for the board windings on Richards Radios it transpired that the cheap DMM i was using was not accurate; it was junked shortly afterwards.

I am now in a position to check accuracy, the movement is not in absolutely perfect fettle but settles with a tap to the facia. (It appears to be unique to this type of meter!)
One thing i can check is the open circuit voltage at the terminals..and i think that i recorded the FSD current of the movement- to be confirmed.

As far as the application of the meter, i did ascertain that the former owner was an A/C fitter in the Royal Navy, and a day later i also bought a duplex 'wee megger' from his descendant.. significantly this also has a high range and a low range. It generated 450v of the full 500v once i had changed the capacitor.

I did wonder whether being an aircraft fitter in this theatre involved messing with Swordfish, Albacore, Fulmar, Firefly, and their associated systems and weaponry. In respect of the Avo, a need to check low resistance without pushing too much current through (or voltage across) a system?

I was going to do a circuit diagram for the Avo but was slightly jumpy about getting it back together and working; i can doubtless map it out later on.

Dave

[Aitor Eneko]

Originally Posted by 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

Thanks very much, i am finding this information very interesting.

[The Philpott]

Avo Low Resistance Ohmmeter

Some readings:

voltage at terminals (voltmeter with 10Meg input impedance)-
Low range- 34-47mV
High range- 28-39mV

Accuracy (reference used is a new UT210 DMM)-

Low range-
0.5 ohm- slightly high at ~0.51-0.52 ohm
1 ohm- spot on

High range-
9.8 ohm- slightly high at 10 ohm

No way to assess accuracy meaningfully above these resistances, owing to the lack of resolution higher up the scale and limited resistor values in my stock, but i am impressed. None of my DMM's has a res. smaller than 100millohm, so the old meter definitely has an advantage in this respect at very low resistances.

(The other Avo i have with a low resistance range is the High Resistance model, effectively a forerunner to the Model 8. In the workshop it enabled me to rapidly and positively identify the COM, DIP, and MAIN terminals on a 12v 60/55w halogen lamp the other day, something my Toolzone DMM was not equipped to do with any certainty.)

Dave

[AndyGilham]

Two more instruments have arrived for the Megger collection this weekend

The Avometer Model 73 (No Serial Number).
Came complete with leather case, leads and user guide

(this goes with my Model 71, 12, 12D and EM272

The second instrument is a Test Set Multi Range No. 1 with serial number 7241-15-664 (June 1964). Based on the Model 8sx Mark II, this includes the shielded (Metal) case and earth stud.


Andy

[pmmunro]

A serial number from a Model 8 Mark I currently on offer on eBay: 21077-C-254.

As these are, as the seller states, quite rare I thought it would be useful to the survey.

PMM

[Sinewave]

Originally Posted by pmmunro

A serial number from a Model 8 Mark I currently on offer on eBay: 21077-C-254.

As these are, as the seller states, quite rare I thought it would be useful to the survey.

PMM

What's rare about it? The date?

[pmmunro]

Yes; the date is less than one year into Model 8 production and there don't seem to be as many in the survey as might be expected from this time.

For all that, auction sellers sometimes tend to think rare means "I haven't seen one of those before".

PMM

[Superscope]

Model 7 update.



Data, for early Model 7's (1936 - 1939) is extremly thin on the
ground, and it has been known for some time that few survive.

I think the main reason for this is simply down to the fact that
not many were actually built in the first place.

I think the reason for this is probably:

The Model 7 was significantly more complex and time consuming
to make than previous models, and I suspect ACWEECO were
not quite ready to undertake the task in Hand and quality suffered, holding back expansion.

I suspect also, the spectre of WWII around the corner meant
resources were being used quietly elsewhere. Research on the
Model 40 and it's variants being probably the main one.



Based on the Data we do have, it looks like the Model 7 could not have
been released before September 1936 at the earliest.


Production seems to have never risen above 100 Units / Month.
Significantly lower than I was expecting.
This production Rate seems to have continued up to and including 1940.

Production then increases slowly in 1941 to around 150 Units/Month.

Full flat out production doesn't seem to have started until 1944 when
around 500 Units / Month were being made.

Production was strong thoughout the 50's but a very definate slowing
down appears to have started around 1964.



Ian

[Superscope]

Following on, from the previous post.

If there is anybody out there, actually interested in this stuff!

Some interesting aspects to the Serial Numbers appear,
once they have been sorted.
For information, I don't intend at this stage to go futher than 1969.

1936 Serial Numbers start sequenctialy
with the Format 7,X(x),Y - Z

In October 1947, the "A" appears in the middle of the Serial Number.

In November 1947, the Format changes to the more familiar ZZZZZ-X(x)YY and Number is reset, possibly even to 1. (We have No 39-A-1147 on record).
This I believe co-incides with the change away from the HorseShoe Movement,
but I haven't received any feedback at all yet to confirm this.

In October 1961, an additional Serial Number Range is added.
Numbers start low and a Suffix F is added.
Both Ranges are run in parallel until at least 1963 when the F range appears to have been dropped.

In 1964 a new Range is introduced, with numbering reset and Suffix F is removed.
Run in parellel with the Range introduced in 1947.

In 1967, a suffix M seems to have been added to 1964 Range of numbers.

In 1970 Serial Number Format and location changes to Sticky Label.



I have no idea yet, what the Suffix F and M's mean.

The Number Range which started in 1947 with the new Format, ran uninterupted
right up until the change to Sticky Labels in 1970.




Ian

[The Philpott]

Yes, we are interested, and yes, i would have halted at 1969 as well!

Dave

[Superscope]

Er!, what!

Sorry Dave, I got down to 1970 and fell asleep!

Anybody that thought that was boring, wait till I start on the Model 40's!

I thought they were going to be straightforward!
WRONG!

Ian

[Phil G4SPZ]

Please keep this analysis coming, Ian, it is indeed interesting and I believe this is what the thread was initially started with the aim of achieving!

[Aitor Eneko]

Thanks!!

My oldest model 7 is 7441-5429

[Superscope]

Thanks Aitor,

Yes, we have that one listed.


Model 7 Production Numbers as follows (Give or Take a margin of error say +- 10%):

Production Rate seems to vary a fair amount, so I guess ACWEECO
adjusted production of different Models to suit the Market as required.

1936 = 269
1937 = 750
1938 = 1044
1939 = 884
1940 = 1187
1941 = 1670
1942 = 2020
1943 = 3892
1944 = 5121
1945 = 5937
1946 = 7596
1947 = 8668
1948 = 6057
1949 = 3048
1950 = 7706
1951 = 13282
1952 = 7096
1953 = 7015
1954 = 6589
1955 = 7576
1956 = 7683
1957 = 4422
1958 = 4079
1959 = 3874
1960 = 4005
1961 = 8993
1962 = 5626
1963 = 5318
1964 = 1180
1965 = 3984
1966 = 2094
1967 = 4484
1968 = 2657
1969 = 3533


Ian

[Sinewave]

Originally Posted by pmmunro

Yes; the date is less than one year into Model 8 production and there don't seem to be as many in the survey as might be expected from this time.

For all that, auction sellers sometimes tend to think rare means "I haven't seen one of those before".

PMM

Speaking of rare, I see a Model 3 sold earlier today at a modest price (still a lot though) for that auction site.

[Superscope]

I missed that one!

That's unlike me, I normally spot the older ones
on my Trawl round EB.

I just did a search and found it.
I guess the Model 8 Mk III description through me off the scent!
I vaguely remember seeing it in a list.


Did anybody spot the Model 4 a couple of Months back, masquerading
as a Model 47A?

I reckon not?

Ian