AVO Multimeter survey

[pmmunro]

Originally Posted by Superscope

Indeed it is Mike. November 1959.
It will be a Mk II.



Still a very useful Device, just not on electronics.
More power orientated.





Ian

To emphasise Ian's point, a high sensitivity multimeter such as the Model 8 causes least distarbance to the circuit under test on voltage measurements but the lower "sensitivity" of the Model 40 is an advantage on current measurements because the resistance between the terminals is less than the Model 8 on current ranges.

For some fault-finding measurements it can actually be useful to have a low impedance meter when measuring voltages in circuits intended to supply significant loads. For example, a high resistance relay contact might be causing a fault under load, but if no great load is in place the voltage will be essentially the open-circuit voltage at the downstream contact.

You just have to have, at least, one of each!

PMM

[The Philpott]

Model 40:

-The attention to details is such that on the circuit diagram the meaning of the letter 'B' is given
(Which relates to the 14 ohm winding part of the 'Q' potentiometer) :

'Meters with letter B in Serial No. copper content 6 ohms. Without letter B, copper content 8.5 ohms.'

The leads supplied with Mike's meter could make it a good buy on their own! The most common issue i have found on Model 7 and Model 40 series is, incidentally, poor connectivity in the Q pot. The meter won't read anything reliably if this happens, and i suspect quite a few were tossed aside for this reason.

Dave

[sparkymike]

My Daughter told me that the seller told her, he was an ex electricity board employee, so that bears out what you said in above post.
Will give you further details when I get it.
Mike.

[sparkymike]

Now have got the meter here (father's day present ) and glad to add that it is in a metal case. Working on AC and DC volts but need to clean up the battery terminals a bit before further testing. Looks to be in good order. Tried to remove it from the case, but very tight fit. Need to carefully lever it out with a very thin metal strip such as a 6'' rule maybe ?
Mike.

[Phil G4SPZ]

Nice Father’s Day present! I like the Mk II version of the Model 7 and Model 40, finding them probably the easiest to operate with the deep selector knobs that are ergonomically good to grip.

The Model 40 has a basic sensitivity of just 167 ohms per volt, but don’t dismiss them completely as ‘no good for electronics’ as I recall at least one 1930s vintage radio service sheet which quoted voltage readings taken with such a low-sensitivity instrument. Used on the higher voltage ranges, loading is tolerable for many measurement points, and even if the pointer deflection is very small, it can still be read with a good degree of accuracy. However the inability to measure high resistance values is, admittedly, something of a drawback...

A strong penknife blade can sometimes persuade the case to separate from the front panel.

[The Philpott]

-Ah, the unavoidable taper in those aluminium cases, a result of being pressed from sheet.
One has to pick out the 'o' ring to give some room to apply leverage.

(Don't forget the Model 40 is also perfect for testing serviceability of PP3 batteries Phil!)

There's arguably only one meter in the range that has more ergonomic rotary switches, and that's the high resistance avometer (late forties early fifties). They have real 'grab'.

Dave

[sparkymike]

I must admit the control knobs are quite tactile with the knurled edges.
If it works ok on the other ranges I may well leave it in its box.
In the past on other model 40's ,I have noticed that there is a small amount of grease on the inside of the boxes, maybe to trap any metal particles from entering the movement ?
Mike.

[Phil G4SPZ]

PMM or Dave will probably know for sure, but I believe that the grease was put there to capture and retain any tiny airborne particles that may have entered during the final assembly process in the factory, and prevent them from entering the movement. The instruments then sat upright on shelves for a time before despatch, and gravity did the rest.

I haven’t seen it on every meter and I don’t know if it was done for specific models or time periods.

[sparkymike]

Perhaps it was done if the meter was returned to the factory for servicing ?
Maybe it was something advised by AVO if meter was being checked away from the factory?
I am sure it would not be a bad thing to do as a matter of course.Just a smear along the base should be enough.
Mike.

[The Philpott]

In at least two of my Model 8/III it appears to be a precise application of sticky stuff much like the goo on fly paper, which does seem to work as well as grease on earlier ones.

I think the biggest (visible!) offender may have been small blobs that get spat out during soldering, stuck somewhere by rosin, which then come loose later on. UK residents will also know about thunderflies (thrips) that at a certain time of year get absolutely everywhere, even inside picture frames. If they meet a sticky surface they're there in perpetuity! Phil's gravity & dust theory also sounds entirely feasible to me.

Dave

[pmmunro]

A model 2 recently sold on eBay. The serial number was reported as 3009.

PMM

[Avo Mk8]

Originally Posted by pmmunro

A model 2 recently sold on eBay. The serial number was reported as 3009.

PMM

Indeed, and it is the meter with a broken range knob that features in this thread https://www.vintage-radio.net/forum/...d.php?t=192059
that I'm now hoping to repair, thanks to Superscope!

[pmmunro]

It's good to know that it's gone to a good home and that it is being given the attention it deserves.

PMM

[majoconz]

I bought my Model 7 very recently from a lady who said it belonged to he late Father and had been in storage for a good few years. It's in pretty good nick in used condition but obviously well cared for - the original Avo style leads have been replaced with something more modern and good quality. It was u/s on first test but responded to some TLC, switch cleaner and a couple of soldered joints needed attention. The cutout doesn't reset without taking it out of it's case but I wasn't aiming to overload it! Its serial is 71142-8701 which I'm told equates to a Model 7 made in November 1942 and was the 8,701th of the line. It has "Standard" engraved above the meter face which I'm told means it may have gone to the Airforce.

[pmmunro]

Martin,

The Model 7 was supplied to British and Commonwealth Forces but with additional type numbers at various times. It is also normal for any Government property to be marked, usually with a "Broad Arrow" also known as a "Feon" https://en.wikipedia.org/wiki/Broad_arrow.

This was certainly used on some Model 'D' Avometers although others had the letters 'A' and 'M' either side of a crown at the top centre of the scaleplate.

However, during the Second World War, the exact niceties of official marking may, just possibly, have been set side in the interests of getting supplies where they were needed.

Several multimeters of this sort of vintage have turned up with the name of individuals either on the meter or its case but it's not possible to say if these were in fact personal property or just instruments taken into close protective custody by the person to whom they were issued.

PMM

[Avo Mk8]

This sold on eBay recently, unfortunately only noticed by me today!
https://www.ebay.co.uk/itm/VINTAGE-B.../275358954107?
I assume a model 3?
Accompanied by an Avo Dapter which I didn't know existed!

I hope someone on the forum was lucky enough to get it

[The Philpott]

'Frying tonight!' I have never seen anything like it. Seems contemporary with the meter in the picture.

Dave

[Superscope]

Sadly it wasn't me that got the Model 3, and I've been after one for ages.

Since there doesn't appear to be a Bid History, I assume it was a Buy it Now,
so it may not have been active for very long.
Somebody got a pretty good Deal in my opinion.

Regarding the AvoDaptor, I've not seen that type before.
It's different to the one I have, which are the ones that normally pop up from
time to time, I assume its slightly later than the one that just Sold.

Even the Box on Mine has a picture of a Model 3 though.

Ian

[Superscope]

I must get myself down to Specsavers!

The AvoDaptor Box I have actually shows a picture of a Model 5
on the Side.

So I think that probably confirms that the one I have is a slightly
later version to the one that sold recently on Ebay.

The one on Ebay is a 4 / 5 Pin version.
The Fifth Pin can be disconnected by pulling up the Knob in the center
of the Five Pin Plug, making it effectively a Four Pin Plug instead.

The Later one I have, is a 4, 5 and 7 Pin version and comes with an
adapter plug.
Typical of Avo of the time, the adapter is very cleverly designed to plug into the
Base Seven pin Socket to make it 4 or 5 Pin Socket, or it can be connected
to the flying lead 5 Pin Plug making it a 7 Pin Plug.

The adapter has two connections on its side to facilitate the Two extra Pins
on the plug in the 7 Pin configuration.


Ian

[Aitor Eneko]

Fantastic adaptor. And very good AVO 3 congratulations to the new owner. AVO 3 is one of the most beautiful son my opinion. Also AVO 1

Here in Spain is very common to see Avo 7, 8, 9 and a few 40 on second hand webs, but no any clue about model 1,2,3,4.