Early AVO Multimeter ID.

[Ben Puylaert]

Dear All,

By change following Avometer in my possession.
Following markings and details.
- Left knob, marked "Switch"
-- Amps: .12, .12, 1.2 and 12
-- Volts: .12, 1.2, 12, 120, 1200
-- Ohms: +, 1000, 10000, 100000, 1Meg
- Three setting screws marked "P", "Z" and "R"
- Right Knob, marked "Rheostat"
-- Three positions: Off, 1.2 and .12 and marking "Amperes" in circular letters
- Dial
-- Lower left corner: "Accuracy B.S.1"
-- Lower right corner: "NO 2020" (The O as upper case)
-- Upper scale: "Ohms"
-- Lower scale: Amperes & Volts"
- Rear side:
-- Extensive "Instructions For Use"
-- "The Automatic Coil Winder & Electrical Equuipment Co., Ltd.
-- Winder House, Rochester Row, London, S.W.1.

My question: which type of Avometer?
Date of manufacturing?
Where to look for a manual?

Regards,
Ben

[ryburn18]

Hello Sir

It looks like you have a AVO Model 40, I used to repair AVO's for 5 years in the 1975's
there should be a divide by 2 in the centre of the face plate. if you switch to .12V DC and press divide by 2 and inject 3mA thats the full scale value of the movement, remember if this has a metal case , some old units did then you have to calibrate the magnetic shunt on the movement in case position, there is 2X 4.5 bell batteries and 1.5 V battery, Megger do do an adaptor for this to fit in the slot.

You might be able to get a manual from Megger Instruments Dover, its an old one , but maybe you could try various Test Equipment outlets all over uk, the manual is not big and it should not cost you too much,

Avo Changed to Megger Instruments years ago so thats where you should start looking first, its and old unit been arround for many years perhaps year 1945 Plus..

The movement alone off hand is 3mA / 60mV with magnetic shunt accross the movement. dont change the series resistance with the movement at all, they never need adjustment unless its been overloaded big time !.

Good luck, they are strong units, one place you can try for a manual is Dowding and Mills Calibration in Stockport, 0161-406-7878 Cheshire, I was there many years long before it was Dowding and Mills,

Well I hope that that helps, if you do clean any contacts, first remove the movement, and be carfull. sometimes dirt gets between the coil magnet and centre core of the movement, a thin long magnetic needle will remove iron dust with the help of a eyeglass, dont take the movement apart, if you it might require the magnet re energizing, and Avo movements on a exchange service can cost over £60...... ! each..clean the glass with a lint free cloth.

The unit new would perhaps cost over £400 expensive, but all hand built. thats was in the 1980's

Good luck..
Regards
Philip

[ryburn18]

Dear Sir

You have a model 40 age from 1945 on,
3 mA movement 60 mV (movement only..) you can check with movement press devide by 2 and inject 3am on the .12V DC range measure voltage accross the movement this should be 60mV +- 1% dont ajust any swamp resistance, magnetic shunt at front of movement for adjustment.

2x 4.5 batteries 1 x 1.5 battery

Best Regards

Philip.........

AVO was later changed to Megger Instruments in Dover... you find info at Megger Instruments, Movenet is rather expensive, to replace, on a exchange basis......

[pmmunro]

Ryburn 18,

I haven't seen you before, so welcome to the forum. I'm sure with your experience, your contributions will be most useful. Having said that, I'm sorry to have to disagree with your identification, which is made more difficult without a photograph.

Ben & Ryburn,

I think the important clues here are the place of manufacture, Rochester Row. This was the second address of the Automatic Coil Winder and Electrical Equipment Company, the first, in 1923, having been Buckingham Gate. Later, the address changed to Vauxhall Bridge Road, which is in fact, I believe just round the corner from Rochester Row. All this, plus the fact that the right-hand knob controls a rheostat makes this a DC Avometer, known at the time as simply "The Avometer".

From the serial number, this would seems to be a very early one, around 1928 possibly. (I am not at home and will check my lists next week when I am). This is the second Avometer, the first having been a small scale production instrument in a wooden case with a part cast aluminium, part ebonite front panel.

With the move to Rochester Row, production began on a larger scale, with the meter redesigned to be built on a Bakelite front panel. This was still a fairly new material at the time. The earliest examples of this model had a cross-hatch pattern on the front panel and an aluminium instruction plate on the back which had a black background and bright print. There was no external fuse, only a short length of wire between two wire supports on the back of the movement. Shortly afterwards, the front panel was modified to take a screw-in fuse of calibrated resistance and the finish was smooth. The instruction plate was revised to the commoner black lettering on an aluminiumm ground.

If my identification is correct, this is quite a rare meter and I would very strongly advise that it should be kept as original as possible and that any necessary repairs are carried out by someone who has the expertise and facilities. I will send you some information of the circuit details when I get home next week. The market value is not great, going by recent sales, but it probably should be.

I very much doubt that anyone at Megger Instruments in Dover would know anything at all about this meter and would only recognise any connection to their company because of the Avometer name and the resemblance to later models. They certainly would have no information or parts.

Best regards,

Peter M Munro

[Ben Puylaert]

Dear All,

Thanks for all information.
I try to attach a picture of my model.
By all presented information I conclude that it is indeed an early model.
Back plate is black with white letters.
However, I believe not in original condition as connectors are of later date.
If wanted I can present more pictures.

Regards,
Ben Puylaert

[pmmunro]

Ben,

This is certainly a very early DC Avometer. Do you know anything about the history of this particular instrument?

The terminal coversion looks to have been quite well done. Originally this meter would have had fixed leads attached to the threaded brass bushes moulded into the front panel. The leads then passed under a moulded bakelite bridge piece which clamped them between the terminal screws. The very first Avometers had rather small screw terminals, but for some reason all other DC Avometers seem to have had the fixed arrangement.

I will get a circuit diagram to you later this week but I have never seen a user manual for these early models.

PMM.

[Ben Puylaert]

Peter,

Some more background about the early Avometer.
But related to my first posting first some corrections.
In the serial number it should be the O as superscript.
The accuracy was referred to B.S.1, however B.S.I might also be possible.

About the history of the meter following information by the person from whom I got the meter.
His grandfather was the first foreign representative for General Radio equipment in Europe. Start 1922 in Baarn, the Netherlands.
The company had also a repair shop.
Based on this information and the fact that much more equipment from that repair shop came into the possession of the family, the grandson assumes that the Avometer
was used as a regular test device.
The Avometer looks as if used in a laboratory.

A mechnical detail to be added to my first posting.
The cover is fixed by seven screws to the body.
A eighth hole is there, but a rivet has been used to keep the cover to the body.
The pit/cavity for the rivet in the cover is larger then the other holes.
So for opening the Avometer I have to drill the rivet.
Was this a normal situation for this type of Avometers?
Related to this and the fact that no original connectors are used, I have the idea that the modification might have been done by the Avometer company themselves.
Our by the repair shop of General Radio in the Netherlands.

Between cover and box there is or better there was a rubber sealing.
However it is that brittle that parts are falling off the moment I start to lift the cover. But the rivet stopped me.
Are spare rubber sealings still available?

Regards,
Ben

[Ben Puylaert]

Dear All,

Some more information about my early DC Avometer.

The rivet as mentioned in previous posting is in fact a small cup in which a small screw is hidden under a layer of laquer.
So now I was able to open completely the unit.
As expected the rubber sealing broke off.

For the inside see pictures.
The movement is protected by a very thin fuse wire. See one of the pictures.
The handwritten serial number is also visible. The same number at rear side of the scale.

On the scale the serial number as well as a cross, just under the O of Ohms.
This cross is part of the ohms calibration in combination with the cross on one of the control knobs.

By accident one of the connectors was loose. It seems to me the original situation, however Peter has given other details.

According to the instruction plate at rear side for all 5 ranges for Volts 6 milliamps gives full scale deflection.

Ben

[SPCh]

Ben,

As PMM has indicated, this would appear to be a very important specimen.
The small lacquer-filled cup was the manufacturer's calibration seal,
(which, unbroken, to collectors is generally worth more than the lacquer's weight in gold !)
However, the "modern" terminals suggest that it has been professionally modified,
so the seal will date from the mod, not from the original manufacture/calibration
which was probably somewhere between late 1927 and mid 1933 (the "Rochester Row" years).

The front panel is very clean and smooth, and predates the "orange peel" texture which has been standard for so long.

The 6mA sensitivity makes it unsuitable for most modern applications, but it's still a lovely instrument, and well worth preserving.

I suspect that a rubber seal from a later model will fit okay, but so far as I'm aware they're no longer commercially available. If you can post the case size dimensions (I'm sure it's "standard" AVO) I'll see if I have a spare one for you.

This instrument should be cherished - I've handled one,but have never owned one - I might even visit you (I'm based "just down the road" in Antwerp) to caress it.

Good luck with it, but be careful !

SPCh

[Ben Puylaert]

Dear All,

Pictures of DC Avometer.

Ben