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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 3rd Jul 2005, 8:53 pm   #61
taipai_royal
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Default Re: AVO Multimeter survey

Hi all,

I have an Avo 7 serial number 7743-10420, does that date the manufacture to July 1943 ?, and therefore a Mark 1?.

Regards Graham.
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Old 4th Jul 2005, 8:47 am   #62
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Default Re: AVO Multimeter survey

Yes spot on, Graham.

Yours was manufactured in July 1943 - the month in which I was born (CF "How old are we ?" thread). A further 25,500 had been made by the time I was four !

Thanks for your contribution
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Old 4th Jul 2005, 9:47 pm   #63
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by SPCh
I presume these numbers are on twin labels, one at top centre of the RH side of the case, and one in the battery compartment below the BLR121.
Thanks for the reply SPCh

It is as you say; this as a late one does not carry a date, I must get back to my old ECR since there was a Model 40 there.
I have'nt searched the forum but what price AVO test leads (covered cup) these days and where.

Yours John
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Old 5th Jul 2005, 8:35 am   #64
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by SPCh
I am trying to compile an unofficial history of the AVO multimeter
Hi SPCh

I thought I should bring to your attention , in case you had not seen it, that in response to a letter in the June issue of 'Television' magazine, appealing for information on the history the AVO, a Mr Conrad Edel replied with some extensive information that may be of interest ... in the July issue of 'Television' page 546.

He describes prodution changes and at one point makes a specific warning about Avo 8's with switches mounted on the front plate, urging that one should never be tempted to take them apart as they will be impossible to reassemble. AVO used special tools and jigs for the job.

It would appear that he was actually involved in their production .. to the extent of attributing a mistake on the scale divisions on early versions of the electronic Avo Model EA113 to himself.

He also asserts that the last figures in the serial number are the month and year of manufacture.

He also publishes his email address there. I am uncertain about the netiquette of reproducing it here.
Nevertheless I hope this proves useful.

Gavin
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Old 5th Jul 2005, 12:03 pm   #65
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Default Re: AVO Multimeter survey

John,

"Official" Avometer test leads are available from both RS (203-5632, 45-00) and Farnell (sorry, I don't have the catalogue to hand). They can also be bought from Avo (Megger) at Dover. If you contact Avo, you might like to buy some spare/replacement terminal caps at the same time.

You may want to pay this price for assured safety but most users are content with less expensive leads.

Gavin,

Thanks for the tip about the article. I would agree that front panel switches need to be treated with great care but not that it is impossible to work on them. In fact, it is a matter of necessity in some cases if a meter has to be repaired. The service manuals give several cautions about working on parts of these meters but the switches don't rate a special mention.

On the earlier post-war models the switches are in two parts; a rotary range switch with a two-part wiper which sandwiches the contacts moulded into the contact ring (rivetted in very early versions) and a function switch with telephone relay type contacts which are operated by face type moulded cams.

The range switch is carried on a die-cast aluminium centre which is pinned to the switch spindle. The two parts of the wiper are separated by nearly square spacers - but not exactly square. If wrongly assembled, the spacer can foul the switch bush making the knob stiff to turn. The exact angle of the wiper tips is also critical to smooth switch operation and should not be disturbed if possible. The tips and contacts do get burnt and sometimes need to be changed.

The function switches can need adjustment and cleaning or replacement. They are just as difficult, or easy, to work on as a Type 3000 relay - except that the adjustment has to be done in situ and the situation is very confined. These contacts have ceramic or plastic lifting pins which are easy to lose. Careful notes and/or photographs taken before dismantling are helpful. Considerable dismantling of the shunt/multiplier boards may be necessary to get access to the switches.

There is no doubt that jigs would be a very useful aid but if they are not available you have to decide whether to devote your time to devising and making jigs to save the, very considerable, time which you will otherwise spend working without them.

PMM
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Old 6th Jul 2005, 9:58 pm   #66
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by pmmunro
"Official" Avometer test leads are available from both RS (203-5632, 45-00)
Hi
Thanks for the input although very good leads for elec plant use (not so for electonics) as you say they are expensive, but Ebay will provide no doubt.

It has disturbed some dust a work both in trying to find 20 yr old leads but reminding me to the general supply of smaller AVO meters of which I know not the model No. ( but aprox 30mm smaller in all axis )

I do wonder if this model was on general release or a special contract.
I will have access for examination to two remaining examples soon, saved from the corporate skip by two thrifty individuals .

Yours John
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Old 7th Jul 2005, 12:10 pm   #67
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Default Re: AVO Multimeter survey

Over the years there were a number of Avo models which were smaller than the mainstream range. There should be some identifying information somewhere on them. Specials were also produced but were rarely adopted for general sale.

The Heavy Duty range was produced from the late 1940s and is described in another thread on this forum. These have a single range knob centrally placed directly below the scale window. This was originally designed at the request of the Great Western Railway before going on general sale with revised ranges.

From around 1960, there was the Model 12, designed especially for auto-electrical work. It is the same size as the Heavy Duty, but in "landscape" format with the range knob at the lower right corner.

The Models 14, 15, 16, 20 and the EA113 were a range of multimeters designed principally for the export market. These too are "landscape" format and most, possibly all, have a blue/grey front panel moulding. Examples of the EA113 and Model 16 have just been sold on ebay.

There were also some "cheaper" meters of an entirely different format such as the 70 series and the EM272. I would have to check which of these were made in Dover. They were superseded by yellow cased types which were produced in the far-east and "suitably" badged.

On the digital side, production started around 1970 with the DA112, a bench instrument using Nixie tubes. This was followed by the DA114, also with Nixie tubes, but portable and about 20% LARGER than the conventional Avometer. Then came the DA116/117 with LCD displays, manually switched and autoranging respectively. As well as commercial sales, the DA116 was an Admiralty/NATO standard known to have been standard issue for conventional submarines. These appear frequently on ebay. The DA117 is less common (and I would like one or an LCD display to suit).

These were followed by oriental digital meters and then an excellent range of rebadged German meters made by ABB/Gossen-Metrawatt-Camille Bauer.

If you can, post some pictures and I would think we will be able to identify the mystery items.
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Old 8th Jul 2005, 11:46 am   #68
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by pmmunro
The Heavy Duty range was produced from the late 1940s and is described in another thread on this forum.
Hi
I seems certain to be a HD AVO I do remember terminals above the meter dial with a nice brown flip over leather case.
As yet those that have them; one just finishes nights and forgot to search for it, and the other is in france watching the cycling for three weeks, so no picture or info yet.
I do know the change over to DMM's did not go well (AVO'S I think), with an increase in burns due to handholding the lighter DMM's.

Yours John (G8JMU)
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Old 8th Jul 2005, 10:09 pm   #69
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Default Re: AVO Multimeter survey

Hi,

I have what I believe is an Avo 9SX, it is ex military but I cannot find serial number, where do I look?

Regards

Dave
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Old 8th Jul 2005, 10:24 pm   #70
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Default Re: AVO Multimeter survey

The serial number on all "Standard" Avometers is at the extreme lower right-hand edge of the scale plate. You may have to hold the meter vertically and look down past the edge of the window.

Most military meters have the serial number in the same place, but there may be variants. Numbers at the left hand side scale plate are usually part numbers for the scale plate itself.

On later meters, from the late 1960s, a figure in the range 1 to 12 at the bottom centre of the scale plate is the type number for the "scale-shape" or law of the scale. The movements were calibrated for linearity and one of the range of scaleplate types which best suited its characteristic - giving an accuracy of better than 1% on direct current - was fitted.

If the movement has been changed, the original serial number should have been written on the new movement's scale plate but this is not always done.

The serial number should be of the form XXXX-(m)m-yy, where m is the month and y the year.
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Old 30th Jul 2005, 9:29 pm   #71
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Default Re: AVO Multimeter survey

I have just had a cheapo Korean meter die from a overdose of HT, Ouch!
So I fancy getting my hands on the real thing at last. I loved the AVOs we had at College when I did Electronics Servicing. (AVO 8 Mk8 I think).
How important is calibration with a older AVO. I have noted some AVO 7s on ebay. Some have screw terminals only, others incorporate socket connections for the probes. About when did they do this?
If I win the one I am bidding on i'll get back to you with the serial number.
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Old 30th Jul 2005, 11:44 pm   #72
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Smile Re: AVO Multimeter survey

Hi Neil
It may please you to know, that unscrewing and removing the terminals on an AVO 7 will reveal a threaded hole-exactly the right size for a standard 4mm plug.
Just be sure not to lose the terminals though!!
I'm sure you know AVO 7=1000 ohms /volt
AVO 8=20,000 ohms /volt


Tim
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Old 31st Jul 2005, 12:01 am   #73
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Default Re: AVO Multimeter survey

I have an Avo 8 Mk5. Unfortunately there is no serial number. I have looked carefully around the edge of the scale but all I can find is a part number.
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Old 31st Jul 2005, 7:13 am   #74
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Default Re: AVO Multimeter survey

A lot of questions, there.

NEIL, the sockets were introduced in 1956 for the Model 8 (MkII), the Model 7 (MkII) and the model 40 (MkII). They coincided with the introduction of new movement magnet blocks.

HYBRID T, the serial number for the Model 8 (Mk V) is on n adhesive labels, usually one inside the battery compartment and one along the right hand side of the case.

TIM, beware: the Model 7 is only 1000 opv while the DIV2 button is held down. At rest it's only 500 opv. Still a beautiful beast, though. For completeness, the Model 40 is only 167 opv (333 opv with DIV2)
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Old 31st Jul 2005, 7:20 am   #75
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Default Re: AVO Multimeter survey

A AVO 7 is only 500 Ohms/volt! Christ!
That must have caused (& will cause) all sorts of problems.
Where will it be marked on the meter what model it is?
I assumed that it was a 7 from the appearance. If I can tell the vendor where to look then I will know for sure. They are disposing of stuff they don't know much about.
Can you get a idea from the appearance of the front of the meter?
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Old 31st Jul 2005, 8:29 am   #76
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Default Re: AVO Multimeter survey

The Model 7 and Model 40 look very similar on ebay photographs:
both have the mushroom pad switches,
and either screw terminals (Mk I) or sockets (Mk II).

The easiest way to be sure is to ask the vendor for the type number as printed at the top of the instruction plate on the back of the case.

If it's legible, the right hand knob of the Model 7 is much "busier" than on the 40: it has CAPACITY and POWER/DECIBELS segmments astride the DC segment.

If you want a serious, sensitive meter, you'd best go for a Model 8 (Mk I, II, or III). There's a lot of them about on ebay, so they're quite cheap. They have the advantage of high sensitivity, and the benefit of youth (post 1950) - you can still get the correct batteries. I wouldn't go for anything later than the Mk III, because after that one, the internal construction became increasingly flimsy.
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Old 31st Jul 2005, 8:34 am   #77
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Default Re: AVO Multimeter survey

PS, Neil,

I just checked on ebay:
you are currently bidding for a Model 40 (Mk II). Sorry.
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Old 31st Jul 2005, 10:33 am   #78
Neil Purling
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Default Re: AVO Multimeter survey

Are there any Web pages with a good family tree of AVO meters?
I will have to findout about the Mk40 specs
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Old 31st Jul 2005, 10:59 am   #79
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Afraid there's not much out there that's easy to access - all bits and pieces. I'll send you some info by PM, and come back to me with any questions. If you let me have your address, I can send you a copy of the Instruction Manual.
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Old 3rd Aug 2005, 6:29 pm   #80
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Default Re: AVO Multimeter survey

Hi SPCh

Further Contribution:
Universal AVOMETER Model 8 Mk3 serial No.8xxxx. 568 (May, 1968?)
casing - modern plastic

from a collegue at work as noted before
A Heavy Duty AVO HD6 Serial No. 0xxxxx4DE 5/84 (May, 1984?)
Scale Range DC 750 - 1.5V. Amps 15A - 75mA.
AC 750V - 3V. Amps 15A - 1.5A
Ohms 0 - 75. at x1 and x100

Yours John
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