AVO Multimeter survey

[Paul Adams]

Well another rare find included when I bought this Avo 8 Mk III, another VC1 Voltage Converter, and the meter only cost £5.00 sold as not working, now working due to corrosion in the battery compartment..

Serial: 89180-1268.

Paul.

[Clivewalker]

Hi,
I have an AVOMETER 8 No 041526

Hope this helps your info.

This meter is still in use, good condition and working fine.

Clive

[threeseven]

Originally Posted by Paul Adams

Well another rare find included when I bought this Avo 8 Mk III, another VC1 Voltage Converter, and the meter only cost £5.00 sold as not working, now working due to corrosion in the battery compartment..

Serial: 89180-1268.

Paul.

Re the VC1, you lucky ***!! I've been looking for one of those for years!

[pmmunro]

Phil,

You're correct in your reading of the date of manufacture of you 36-range Avometer. It's good to know it's all working as it should. Quite often the high voltage multiplier windings are open-circuit - and there's a awful lot of wire in them, something of the order of a kilometre if my calculations and wire tables are correct.

Clive,

Do you have more information on your Model 8 please? This looks like a Model 8 Mark V serial number, otherwise the number needs a month & year prefix.

PMM

[Phil G4SPZ]

A question has arisen (post #45, this thread) about whether Avo continued to manufacture and sell the original Avometer Model 7 (which we know as the "Mark 1") even after they had launched the Mk II.

The Mk II was apparently released in 1948, but I have a Mk 1 dated 1950 and another Forum member has one dated 1953. Were Avo simply using up old-stock Bakelite front panel mouldings? Or perhaps movements have been swapped but the serial numbers not changed over?

I bet PMM will know the answer to this one!

[russell_w_b]

That member is me.

I'm also curious to learn why the change from non-power factor measurements to the extra sockets and components used in conjunction with the PF adaptor unit didn't result in another 'Mark' of AVO 7 between the Marks I and II.

Perhaps AVO used their mouldings to best economical effect, as you say? I have a 1975 AVO 40, and it is obvious that the moulding is the same as a 7 Mk:II. There is no model or mark number on the little spot in the centre, making it suitable for either instrument, thus rendering it more economical to produce variants.

[pmmunro]

Phil, Russell,

I'm away from home just now so I don't have access to a full range of literature at present.

I think there are several issues here and it is probably fair to say that ACWEECO were never very consistent in their use of 'Mark' numbers.

During the early 1940s, ACWEECO appear to have used whatever front panels were to hand for Type 'D' Avometers. The priority would have been to get the instruments out and in use and who could say what would matter in even a few days ahead?

Given the length of the production run of the Model 7, it is certain that many of the meters still around have had their movements replaced at some time. Officially, the original serials number should have stayed with the instrument when the movement was replaced but there must have been many cases where the owner's service organisation used serviceable movements from damaged meters to repair others. The priority would have been to return working instruments to use with little or no regard for the kind of historical accuracy which interests us. I have several meters whose back-case is obviously wrong for the meter inside for similar reasons. I suspect that to some people this did not matter at all - they were probably of the mindset which disregarded instruction plates and such details, perhaps even issues of accuracy.

Then there is the issue of matching scaleplates to movement characteristics. We know this is important, but for the casual repairer, who possibly knew no better or didn't care, this would not have mattered.

One of the first Type HR Avometers I acquired has Model 8 Mark III movement, apparently factory fitted, complete with the original scaleplate, matched to the movement characteristic, we would hope. The small block magnet and the thermistor pointed to this anachronism.

My outlook is that an Avometer, or any other instrument, should work to specification but how many users were quite happy to have something which was vaguely correct and didn't care if "rough" meters were mixed with calibrated ones? This makes an interesting comparison with the culture of Unthinking Quality Assurance (UQA) where everything has to be calibrated, even if it can, in reality, only be verified. How do you re-calibrate a steel rule? I believe that quite a few good instruments, including Avometers, have been scrapped because in the world of UQA, it was not considered worth the expense of having an "old" meter sent for calibration. (After all everything made more than 3 years ago is old and if it's not digital it's antique).

I recently resurrected a Model 8 Mark V which was condemned as "beyond economical repair" for a user who much preferred it for his application. One of the replacement, fused, test leads had a faulty (not blown) anti-surge fuse.

When I have more information to hand I will attempt to set out some form of Model 7 chronology.

PMM

[russell_w_b]

Excellent, PMM - many thanks.

[Derek1960]

Hi
Have recently aquired two Avo8 mk5 Meters the serial no's are
s/n 05209
s/n 08981

[Clivewalker]

Hi.

Ref post 983

The info on the AVO reads, FC No 041526 8V this is on the side casing and also in the battery compartment.

Hope this helps.

Clive.

[Phil G4SPZ]

Originally Posted by pmmunro

...many of the meters still around have had their movements replaced at some time. Officially, the original serials number should have stayed with the instrument when the movement was replaced but there must have been many cases where the owner's service organisation used serviceable movements from damaged meters to repair others.

This is possibly true of my latest acquisition, a very clean fully working ex-GPO Model 7 Mk 1, on which the serial number has been partially obliterated. Who would do this, other than the owner's service department... or perhaps the individual who liberated it from its original owner? The best I can do is to report the serial number as 2xxxx-A-551.

Inside it is pristine. It has no "P.F." sockets. The movement has a block magnet, and the scale plate power range has the clearest red lettering I've seen to date. It even came with a D-cell dated 2003 which works perfectly! I think this instrument has been protected in its leather case and given little use.

[Paul Adams]

Congratulations Phil on your latest acquisition , I have another oddity as someone has also gone to great lengths in removing any ID from this model ‘D’, all that can be seen in small lettering is the word avometer in the bottom RHS of the scale plate.



Oh and another acquisition an ex BBC model 71, complete with case and leads, the only serial number that I can see is: 274883 indented on the scale plate.



Paul.

[russell_w_b]

The BBC Riggers used to use those AVO 71's at Skelton.

[Phil G4SPZ]

I really must abandon my one-man campaign to acquire and restore every available Model 7 Mk 1... but for now, here is the latest. Serial number 71040-A-4591.

This is a bit of an oddity as its serial number dates from October 1940, yet the movement is the much later type with red block magnets, so I guess it has had a replacement movement at some stage in its life. The insides are otherwise untouched, with no sign of any other components having been replaced, and after cleaning a few contacts and rheostats it works perfectly and is 100% accurate.

[ex seismic]

Avo 7; it doesn't say Mk 2 anwhere so I assume it is a Mk1, serial number off the scale plate is 46173-A-154. Top centre on the smooth border is 10S/1 and a WD broad arrow.
The instruction plate on the back is p/n 20670/7.
I have repaired one broken wire and all appears to be working.

Gordon.

[Phil G4SPZ]

Having virtually run out of space for any more full-sized Avometers, I've started a "minor" collection of Avominors:

DC Avominor s/n 86238-1246 (December 1946?)
Universal Avominor s/n U128444-254 (February 1954?)

The DC model reads 10% low on all ranges, so needs a bit of attention, but the Universal is remarkably accurate. I've yet to make sense of the 'low ohms' range though - can anyone explain how to interpret resistance readings taken in this mode? They work 'backwards', i.e. an open circuit gives FSD and a short circuit gives almost, but not quite, zero pointer deflection.

[Paul Adams]

Bought one that actually works for a change, I seemed to be plagued by movement faults at the moment.

Model 8 Mk 5, s/n: 8v/12/73.

Paul.

[Paul Adams]

Another addition to the collection, and just in time for my birthday.

Serial: 7742-7836 (7Mk1).

Paul.

[Phil G4SPZ]

Paul,

Can you decipher the serial number to ascertain the date? Is it July 1942 or August 1936? I suspect the former, but wouldn't it be nice if it were the latter?

I'd like to add to the survey Universal Avominor serial number U127415-1153, 8 months younger than me but in worse condition, with a sticking movement!

I've just realised I've made the 1,000th posting to this thread. It's slowed down of late, and I wonder if it will reach 2,000?

Phil

[pmmunro]

Paul, Phil,

I think this serial number has to be from July 1942 as the pattern at that time was Model-Month-Year(2 figures)-serial number.

The Model 7 was introduced, at least to the public, in August 1936, so I would have expected a very low serial number if it was from 1936. During the 1930s, there was just a single year number, e.g 13-919 is a 20-range Universal Avometer from January 1933 and 729-2613 is a model 7 from February 1939.

I acquired one with a very similar serial number, 7442-7314, in very poor condition, including a warped front panel which would take some explaining. This would suggest that production was running at around 500 meters per month, but this might be all Avometers or just Model 7s. However, another from the end of 1941 has the serial number 71241-6532 which is nearer 200 per month. Perhaps production was concentrated on Model 7s in April?

Model 7 Avometers from the 1930s seem to be very rare, much less common than any other Universal Avometer from the same decade.

PMM