AVO Multimeter survey

[Phil G4SPZ]

With the aid of a bright light and my strongest ready-readers, I've now found a serial number - 58810 - but not where PMM suggested. It was impressed into the rear of the case!

Phil

[Dynamo]

A bit late maybe but here we go:

Model 8 : 128908-C-1061
Model 8 Mk3 : 37420.266
Model 7 : 51660-7/175
Multinor Mk5 : can find no serial number

[calum]

hi,

Here's a few from a friend of mine:

Mk II 73952-558
Mk II 140383-C-552
Mk II 11179-365
TS-1 6116

also a Mk V, but no number can be found. Any idea where it might be hidden?

[Phil G4SPZ]

Just acquired, an Avo Model 7 Mk 1, s/n 15217-A-550.

Cost - £2.20. Reason - faulty movement! Will post a 'help' request elsewhere.

Phil

[SPCh]

calum,

Serial numbers for the Model 8 Mk V were normally on adhesive labels:

one at the top centre of the right hand side of the case,
and a duplicate in the battery compartment.

(By this time the S/N was no longer a part of the instrument's personality and history,
but more an afterthought that was "bunged on before it went out the door")

[calum]

thanks much...

[peulanse]

SPCh,
My AVO: Model 8. No. 126843-C-861
Between the knobs, above the cut-out there is another marking: "8 MkII"
This instrument came available (for 5 Dutch Guilders) during a lab upgrade.
I also have a manual, but it is for MkIII. Backside right under: "15000-12-64".
Frans

[SPCh]

Thanks, peulanse.

The Mk II. is very similar to the MkIII in your handbook.

The configuration is essentially the same, but with a few component changes in the AC and OHMS sides.

The Mk.II rectifier is a true (4 diode) bridge,
whereas the Mk.III uses 2 diodes + 2 resistors;

The Mk. II has a single-resistor swamp
(as opposed to two resistors and a thermistor).

If you have any detailed questions feel free to PM me,
or if you care to send me your postal address, I'll send a photocopy of the Mk.II schematic.

Happy measuring.

[Alan Stepney]

I have several Avos.

8 S/N: 37936-763D
8 Mk 3: S/N: 101560-869

A couple more 8's, a 7 and a 40, all of which are stored at my sons house.
(Might still have an Avominor there too.)

[calum]

Originally Posted by calum

also a Mk V, but no number can be found. Any idea where it might be hidden?

Found it, thanks:

GC No 0043587
8V

I didn't realise that the Mk.V was still around in 1987, if that's what that denotes. Appreciate this one might be a little too new for inclusion in the survey.

[ian old]

hi
just dug out multiminor mk4 must have been in shed 30 years ex mod no 6625-99-102-0122 number impressed into top of case 40651 hope this is of some use
ian

[Phil G4SPZ]

My latest acquisition was described as a Model 40, but I think it's earlier. The serial number is 27-6238, it has 20 ranges and a fuse, and it says Universal Avometer on the front. Could this be a Model 3?

Phil

[SPCh]

Phil,

The serial number is certainly consistent with a 20 Range AVO from February 1937.
(AVO never called "Model 3", although that's what it was).

If it is a Model 3, it should have 12-based voltage & current ranges,
and four resistance ranges (1K, 10K, 100K & 1M)
only the lower two of which work on the internal battery.

[Phil G4SPZ]

Yes SPCh, thanks, that's the one.

My third full-size Avo arrived today, a Model 40, serial number 83505 40/10/78. Having read through nearly all this thread, this instrument would appear to be one of the latest Model 40s. It has P.F. sockets (what were these for?) and the serial number appears not on the scale plate, but on an aluminised label on the right-hand side of the case.

After re-fixing the plastic window in position it seems to work perfectly.

Phil

[pmmunro]

You have probably successfully, unwittingly (and surprisingly), misled my learned friend SPCH over the serial number and date. (Why should only the lawyers got to call each other LFs - SPCH is as well eductaed as any of them).

If the meter has a serial number with 27 as its leading figures it seems very likely that it is from August 1937, but does it have a divided by two button? If it does then it's not a 20-range meter but a 36-range one. The 20-range was, as far as my research and memory serve, superseded in 1933 by the 34-range meter which in turn became the 36-range version. It couldn't be 1927 as the first Universal Avometer was the 20-range in 1932 and by 1947, the serial numbers had the later pattern. All of these had fuses.

PMM.

[pmmunro]

The PF sockets on your 1978 Model 40 are for connection to the optional Power Factor Unit described in the Model 40 manual (and very seldom used, I would guess).

You state that you have refixed the plastic window - surely it should be glass?

The trouble with a plastic window is that it can attract a static charge and that will affect the long knife-edge poiter of an Avometer - in effect a combination of moving coil instrument with electrostatic error source.

There was a thread a few weeks ago about refixing meter glasses - my own preference is for one of the modern specialist epoxy adhesives designed to fix glass as I assume that it accommodates differential thermal expansion amongst its merits. In default of a spare glass, it should not be too difficult to get a local glazier to cut you one to match a pattern - the plastic replacement of a stiff card.

Essentially this meter is a direct development of your 1937 meter using a block magnet movement instead of the horseshoe magnet type, a cut-out instead of the fuse, improved switch design and component resistors instead of wound coil resistors.

Of these features, most are improvements but the type of resistor is debatable. The wire coils are more stable but very delicate, as you have found, and expensive to produce. The component resistors do sometimes drift but are much easier to handle without damage.

PMM.

[Phil G4SPZ]

Originally Posted by pmmunro

You have probably successfully, unwittingly (and surprisingly), misled my learned friend SPCH over the serial number and date

Well, sorry to have unwittingly caused confusion in court, m'lud! 27-6238 does indeed have a divide-by-two button, and its serial number appears printed on the front of the scale plate as well as written in pencil on the back of the scale, together with the name "Ron". However it very definitely has only 20 ranges, as follows:

DC volts: 0.12, 1.2, 12, 120, 1200V
DC amps: 0.012, 0.12, 1.2, 12A
Ohms: 1000, 10000, 100000, 1Meg
AC volts: 12, 120, 480, 1200V
AC amps: 0.12, 1.2, 12A

Reading the circuit of the 20-range Universal Avometer, there are indeed some differences, such as the divide-by-two button, but the movement has a measured resistance (including swamp) of 18.1 ohms, not 13 ohms as shown on the circuit.

The faults with this meter include reading roughly twice the correct applied DC voltage on the 1.2 volt range, and no readings on other DC voltage ranges.

The case is metal, has a black crackle finish, with an integral wooden battery case for one 1.5 volt cell. I suspect the case is not original, as the instructions on the back describe 34 ranges - more than exist on the meter.

I suspect that the movement, which has a black horseshoe magnet, may have come from another meter, and I would very much appreciate the assistance of the Avo Forensic Team in identifying this instrument. Sorry to pose such problems; this may be yet another hybrid meter like my Multiminor Mk 2/3/4 which sparked my interest in AVOs in the first place!

Kind regards,

Phil

[Phil G4SPZ]

Originally Posted by pmmunro

The PF sockets on your 1978 Model 40 are for connection to the optional Power Factor Unit described in the Model 40 manual (and very seldom used, I would guess).

Thanks for that.

Originally Posted by pmmunro

You state that you have refixed the plastic window - surely it should be glass?

No, I'm sure it's plastic... it feels lighter and very different to the glass in my earlier 20-range meter. I was reluctant to remove the movement in order to get at the window, so I have temporarily secured the window from the front of the meter with a few spots of superglue.

Phil

[SPCh]

Ah ! The dangers of hearsay evidence !

As PMM rightly states, if it has a DIV2 button it's certainly NOT a Model 3,
but NOR does it have 20 ranges.

However, one of our number has (or claims to have !) a Model 3 from December 1935,
and its serial number is consistent with a (statistically verified) production volume of 100 to 150 per month throughout the product's lifetime to that date.

Your Model's serial number would seem to continue that trend for the intervening 14 months,
(and I have no EVIDENCE as to when Model 3 production stopped - the Survey is thin on Models "3", and totally transparent on Models "4" and "5".

Clearly I shall have to sub poena (by PM) the witness for the December 1935 exhibit.

Perhaps PMM would see me in chambers ...

[Phil G4SPZ]

Hmm, interesting... Have Counsel yet concluded what my strange 20-range Avometer with a DIV2 button is, then? I can forward photographic evidence if this would assist the jury to reach a verdict.

Thanks for all the interest, by the way!

Phil