AVO Multimeter survey

[AndyGilham]

Just received a new DC Avominor. This is an early straight edge version in perfect working condition and complete with case and leads. There is also a repairs receipt from 1991.
The serial number is 8190-14 (January 1934)

Andy

[pmmunro]

Two more Protimeter serial numbers for the collection: 285-657 and 443-285.

There are significant differences between these two instruments so there are more variants to be considered.

There are two switch settings: on the 1957 meter, these are marked "Check" and "Test", while on the 1958 version the markings are "Reset" and "Test".

There is also a strange difference between the "Brick" scales. On the earlier meter, there is a short green sector, up to the 18% mark on the "Timber" scale and the legend "Dry" up to the "20" mark. On the later meter, the green segment is badly faded but is marked "Damp" so it would seem that by 1958 there was no dry brick.

Scans of the instruction cards which each meter had in the lid of their cases are attached. Note that the cards state that spare prods are available from "the makers". To the user this would have meant Protim but the "Avominor" legend moulded into the front panel may have been a bit confusing, assuming the user knew of the existance of AVO/ACWEECO.

I had always assumed that these meters were custom made by AVO for Protim. The serial numbers certainly suggest that hundreds of them were made and, without removing the internal back panel, they look professionally produced. My inclination is to think that they were made by AVO.

The use of the Universal Avominor case some time after the Multiminor was in production also suggests that the Protometer design was drawn up some time in the early 1950s.

Companies were probably less hasty to scrap tooling as soon as its main product ended manufacture than now, and it would seem the Universal Avominor tooling still existed in the later 1950s.

It seems that Protim still exist, though now amalgamated with Koppers - https://www.kopperspc.eu/products/protim.html and trading as Protim Solignum Ltd, Fieldhouse Lane, Marlow, Bucks, SL7 1LS.

You can still buy a Protometer, althought he form has changed a bit. However, the AVO cased version does appear in the literature; https://www.protimeter.com/assets/do...052419-web.pdf.

Clearly Gerald Gobert, needs some more research.

PMM

[Superscope]

PMM, Mike,

Thanks for the new Information.
It's all starting to build up a picture of this elusive Meter.

Great that we now know of Five surviving examples. Well, probably only Four and a half in reality!

I certainly found Protimeters still available when I was researching them, but I never spotted that Gem of historical information in their Catalogue!

I wonder if the Company still have an original Protimeter themselves.
They must have got their Photo from somewhere?



Ian

[ex 2 Base]

I watched channel 4 last night at 8 O'clock , all about the British Nuclear bomb program and notice two AVO meters, when a picture of the bomb site in Christmas Island was shown.Looked to MK 8 and new, I hope they escaped and are still happily working.Ted

[Sinewave]

MK8?

[AndyGilham]

Regarding the on going protimeter instruments discussions. It is a interesting instrument so I have had a nose in the archives, and I can tell you there was another version manufactured by Avo, the Multiminor Protimeter Mk2A...... Anyone seen one of them??

Andy

[pmmunro]

Andy,

Did your archive research reveal any information on the Mk 1 Protometer, especially circuit information?

I don't think I've seen a Mk 2 (Multiminor based) Protimeter, but I do have two other variants on the Multiminor theme: the International Rectifier/AVO Zener Diode Selector and what seems to be a temperature indicator labelled "Aeration Systems (NCH) Ltd.

The Zener Diode selectors have serial numbers 161-763 and 233-763. I'll start another thread on Multiminor based special instruments when I get some time.

PMM

[AndyGilham]

PMM,
I have had a look, but do not seem to have a schematic anywhere.

I have looked into the protimeter a little more this morning. It seems the Multiminor Protim came in 3 different variants.
1. The Protimeter Mark 2A
2. The Protimeter Mark 3
3. The Protimeter Grain Master

See the attached drawing from May 1959. Interestingly the 2 selectable options for the range are RESET and USE. For the Universal Avometer Protimeter, i see the same range names, not the 'TEST' or 'CHECK', but the word 'USE'
I do believe there were a number of variants of those

1. Universal Protimeter with 'CHECK' (Left Side) and 'TEST' (Right Side) - Early 1956
2. Universal Protimeter with 'TEST or USE' and 'RESET' - January 1958
2. Universal Protimeter with 'RESET' and 'TEST or USE' - January 1958
3. Multiminor Protimimeter Mk 3 - February 1958
4. Universal Protimeter with 'TEST' and 'RESET' - March 1958
5. Multiminor Protimimeter Grain Master - July 1959
6. Multiminor Protimimeter Mk 2A with 'RESET' and 'USE' - May 1959

Andy

[AndyGilham]

All gone very quiet here...... ��

Andy

[Phil G4SPZ]

We’re all reeling from the shock of seeing that huge range of previously unknown Protimeters that we’re suddenly going to have to start collecting...

[Superscope]

I'll second Phil's comment!


Ian

Yes, a very good discover that model!!

[Sinewave]

I went to Hendon museum yesterday. I've been a few times but didn't notice before that in a display cabinet there's an Avometer!

It's a Multiminor, serial No. E 7638 194.

[micheal]

Another obscure Avo Mulitminor variant, the International Rectifier/Avo Zener diode meter
serial number 179-763.
Not really sure what this meter is all about. just zener didoes and the ability to measure the current through the zeners.

Mike.

[AndyGilham]

Originally Posted by Sinewave

I went to Hendon museum yesterday. I've been a few times but didn't notice before that in a display cabinet there's an Avometer!

It's a Multiminor, serial No. E 7638 194.

That is the Universal Avominor, not the Multiminor.

The serial numbering for the Model E variant included a sequantial code, a hyphen and followed by the year in full. So -194 does not seem right, i would expect another digit. I have added that to my growing list of these model E variants and have 16 in total. If i order them by serial (sequentail) number, it wouldimply this instrument is from 1943. (E 7638-1943)

Andy

[Superscope]

Mike,

Would you happen to have any photo's of this International Rectifier/Zener Diode Meter?

Is International Rectifier the Name of a Company who may have Sold the Device I wonder? Like Protimeter.
I remember from Years back a Work Colleague who's Girlfriend worked for a Company called "International Rectifier".
Needless to say, he got the Mickey taken big time that his Girlfriend worked for International Rescue (FAB!)
Well, it was funny at the time!


Regarding the Model E, I was going to ask how that would be Dated.
Might just be that the 3 didn't print out correctly.
Not something anybody would have particularly worried about at the time I guess.



Ian

[Refugee]

International rectifier sell the original IRF840 MOSFET as well as a wide range of rectifiers.

[The Philpott]

The serial numbers from various Type E avominors indicate that there was more than one series of numbers applied to the scaleplates...with no discernible difference between the meters involved. Reason unknown..

Dave

[Sinewave]

Originally Posted by AndyGilham

That is the Universal Avominor, not the Multiminor.

Yes indeed, my mistake.

[micheal]

Hi Ian the full company name is International Rectifier Company LTD.
Sorry can not supply any pictures because i do not have that facility, but is AVO Mulitminor MK4
beige case but with ranges substituted for the value of the Zener diodes, (i think 3.7v to 30v
i'm away from the meter at the moment and can not check).
The zero ohms knob is same style but is now a push button which you press too read zener current.

Mike.