AVO Multimeter survey

[Phil G4SPZ]

And a stepped-sided case:

Phil

[AndyGilham]

Originally Posted by Phil G4SPZ

I thought I’d dust off my collection of DC AvoMinors. In order of appearance:

2712-24 (small knob, flat sided, 6, 120, 300V)
3597-113 (that’s definitely what’s written on the scale plate, but should it be -114?)
40955-16 (small knob, step-sided, 6, 120, 300V)
73856-943 (large knob, step-sided, 6, 60, 300V)
89534-647 (as above, but marked “ PROPERTY OF MIMCO LTD”)

Phil

What about instrument 9712-24? You posted that serial number back in post #1021. Or is that a typo and should be the 2712-24?
Logically for dates, it should really be the 9712-24 serial, as that fits in with the 1934 models.

Regarding 3597-113 serial, I am sure that is correct (January 1933). I have instrument from January 1934 that are much higher serial numbers (7378-14. So again, logically it fits in well with November 1933 products. I have another from November in the same region (3232-113)

Andy
)

[Phil G4SPZ]

Ah, yes, sorry Andy! I’m guilty as charged, m’lud. 9712-24 is correct. In my defence, the style of the lettering makes confusing the figure “9” for a “2” an easy error to make.

[Superscope]

That's a nice collection of DC AvoMinor's Phil.
Do you have any in their rather nice Wooden Felt lined Boxes?


Thanks to all who have responded to the AvoMinor Clarification Call.
So this is my current understanding based on previous responses:
Please Jump in and correct this if this is still incorrect.

Original DC AvoMinor (Square Box Style Straight Side and Stepped Side Variants)

1. DC Avominor (standard)
2. DC Avominor HR (High Resistance)

Model 1 (Universal AvoMinor),

3. AvoMinor (Standard)
4. Type H (Military version)
5. Type U15 (Military version)
6. Type E (Not a Model 1 per se, but does use a Model 1 Style Case)

Model 1a

7. Only one Standard Version known (Model 1 Style Case)

Model 2

8. Only one Standard Version known (Model 1 Style Case)


Ian

[Phil G4SPZ]

Originally Posted by Superscope

Do you have any in their rather nice Wooden Felt lined Boxes?

Yes Ian, the straight-sided meters have felt-lined wooden boxes. I’m sure these have ensured the survival of the meters, which in most instances have their original test leads and prods still intact. The step-sided meters came without boxes.

In fact, I have a spare felt-lined box if anyone would like it. It only fits the straight-sided meters though.

The MIMCO meter came in its own brown leather case which also has space for the leads and prods, and is marked “MIMCO” on the lid. It’s quite nice and looks like a smaller version of the case that fits the Universal AvoMinor, and is made of thicker leather. Clearly Marconi’s bought lots of instruments from Avo and could have them personalised. I also have a full-sized Model 7 engraved “Marconi”.

[AndyGilham]

That's all looking good Ian.
Just a few additional comments from me regarding the Universal Avominor.
From my gathering of serial numbers, it seems the Type H (10S/46) instruments were part of the standard (Model 1) serial numbers.
The Model 1A, Model 2, Model E and Model U15 had their own serial number ranges.

So in total there were 5 different serial number ranges incorporating the 6 variants.
of course you also had the Protimeter, of which at least 236 were sold!


My 3 Avominors are all in the felt lined boxes, they really did a good job protecting the instruments.

Phil, during the 40's and 50's ACWEECO supplied Marconi with movements for their equipment, so there was a strong relationship between the companies.

Andy

[Superscope]

Hi Phil,

I would hang on to your Spare AvoMinor Box!
You never know when another DC Minor without a Box might ambush your Collection without Warning!

I have resisted the temptation to collect another branch of Avo Meters thus far!


Thanks for that extra information Andy,

Which brings me neatly to my next question which I was planning to ask.

What exactly is the Protometer?
And does anybody have a Photo of one they can post?

I am guessing this is not the same device as the Low Resistance Ohm Meter under a different name?


Ian

[micheal]

The type E is a DC only AVO used by the Air Ministry with two types of case the first has the usual crackle finish front the second has a completely shiny smooth front.

Mike

[AndyGilham]

Originally Posted by Superscope

Hi Phil,

I would hang on to your Spare AvoMinor Box!
You never know when another DC Minor without a Box might ambush your Collection without Warning!

I have resisted the temptation to collect another branch of Avo Meters thus far!


Thanks for that extra information Andy,

Which brings me neatly to my next question which I was planning to ask.

What exactly is the Protometer?
And does anybody have a Photo of one they can post?

I am guessing this is not the same device as the Low Resistance Ohm Meter under a different name?


Ian

Ian,
I have attached pictures of the protimeter. Its the Universal Avominor case, with most of the sockets being blanked off

[Refugee]

That protimeter looks like the sort of item a damp proofing salesman would have to show off to potential customers.
The scale plate shows timber and brick and nothing that would allow a user to use a regular meter on ohms range as a substitute.

[Superscope]

Thanks for posting those Photo's Andy,

I knew of their existence, but have never seen one before.
That's an interesting device.
Is your Photo part of the Megger Museum collection?


We only had one logged on this Survey before your recent AvoMinor List,
and that belonged to Mike.
Serial No 593-958, so I guess it is likely that nearer 600 were made.
We now have Three Recorded.

So, was this an Avo Meter in the true sense, or something built for and to a Client Specification?
Or was "Protim Ltd" an Avo Company I wonder?



Mike,

Thanks for the extra info on the Type E cases.

I know the Type E is DC only, but to avoid confusion with the
earlier DC AvoMinor, I will refer to it in the Survey Document as a Model 1 Type E.
As apposed to a "Universal AvoMinor" Type E which would add to the confusion.

Do you still have your Protimeter?



Ian

[micheal]

Hi Ian, yes I do complete with case and leads exactly as shown in post 2329

Mike.

[AndyGilham]

Originally Posted by Superscope

Thanks for posting those Photo's Andy,

I knew of their existence, but have never seen one before.
That's an interesting device.
Is your Photo part of the Megger Museum collection?


We only had one logged on this Survey before your recent AvoMinor List,
and that belonged to Mike.
Serial No 593-958, so I guess it is likely that nearer 600 were made.
We now have Three Recorded.

So, was this an Avo Meter in the true sense, or something built for and to a Client Specification?
Or was "Protim Ltd" an Avo Company I wonder?



Mike,

Thanks for the extra info on the Type E cases.

I know the Type E is DC only, but to avoid confusion with the
earlier DC AvoMinor, I will refer to it in the Survey Document as a Model 1 Type E.
As apposed to a "Universal AvoMinor" Type E which would add to the confusion.

Do you still have your Protimeter?



Ian

Ian,
No I am afraid I do not own a Protimeter. I have serial numbers for 2 though. One I found a photo of online that has been converted into an ugly lamp, and the other owned by a member of another forum.

I am pretty sure Avo never assembled this product, I'm sure we just supplied the machined panel and some addition parts. I'll look into that.
Certainly not a company owned by Megger.

Andy

[The Philpott]

Immaculate Protimeter! I too saw the one for sale a few months ago which had been vandalised. I'm curious as to whether the movement is wound to a unique spec. or whether it is the Model 1 item (2.5mA FSD gross) As the unit measures high resistance this suggests it could be a high impedance low consumption movement- i successfully use an Avo 8 MkIII as a rudimentary damp meter using two probes set around 3/8ths inch apart. M seems to blame the Avo for the fact the carpet is damp in one place (shooting the messenger, hardly fair..)

Note that the Type E (Air ministry) Avominor is the only unit i'm aware of that has a fuse -similar to early big Avo's. As usual the fuse must have a resistance of it's own to ensure correct readings. Predictable the taps and dies used to cut the fuse threads wore with use, and this is possibly the reason that i have encountered a fuse which only fits it's own Type E...although it could be down to incursion of solder into the area where the threads mate, necessitating a finishing-tap at the factory. I have one Type E which smelt strongly of turret oil when initially removed from it's case. Although hydraulic, multi-gun turrets of the period did have electrical switching.

Dave

[Superscope]

I never saw the Vandalized Protimeter unfortunately.
I don't generally keep an Eye out for that Style of Meter.

If it happened to be on good old Ebay, does anybody know the Item Number of the
listing, or the Title they used to List it?
I would be interested in seeing the Photo's.

I guess this is where SteamPunking is the most Damaging!

That will be the second time this Year then, that an extremely Rare Avo has been Victim,

The number of Alloy Cased Model 7's that have been Steampunked recently is a shame when
so many Later far more common Bakelite Model's are available.
Although, I guess the SteamPunker's are generally looking out for the Metal Bodied ones!



Regarding the Protimeter's sensitivity, I guess only Mike might be able to shed any light on that one.




Ian

[AndyGilham]

The converted lamp was not on eBay, it was on etsy...... And it is still available I believe.

www.etsy.com
Listing: 258872406

Andy

[Superscope]

Thanks Andy,

Unbelievable!

They have even destroyed the Leather Case.
Wish I hadn't looked now! that will teach me.

I guess I was holding out hope that it might be able
to be saved, but I doubt that now having looked at the Photo's.

So One of only Three currently known to Survive and this has been done to it.



Ian

[The Philpott]

...One good thing about vandalised instruments or gear that remains unsold for a lengthy period - it either indicates rampant over-pricing or a limited market for the product. If however one is sold the creator then makes three more.

The (homebrew) Universal Avominor ply box i mentioned previously:

I rather like the scallop provided for the zero ohms pot. I had a grin at the tolerances though- no allowance was made for the rubber feet when the height of the meter was measured- fortunately the base is 14mm thick so it was merely a case of drilling some depressions inside. (This is exactly the sort of mistake i would be apt to make if tired when tailoring something to size!)

Dave

[micheal]

Regarding the Protimeter's sensitivity, I guess only Mike might be able to shed any light on that one.

Details of Protimeter it uses two 30volt batteries type B123 = 60volts.
Series resistance of 177K ohms including zeroing pot.
So sensitivity is 339U/A (probably 340U/A in reality).
So could be Universal AvoMinor Model 2 MVT shunted to 339U/A.
The meter is dated Sept 1958 so the time line is correct.

Made by AVO & instruction say distributed by PROTIM LTD. 356-368, Evelyn street,
London, E8. Phone number TIDeway 4611

Mike.

[The Philpott]

Thanks Mike. At least that means that an o/c movement alone, in a Protimeter, would not necessarily relegate it to display only. Due to the non-critical scale-shape it seems a slightly worn/jittery Model 2 movement would suffice.

The proliferation of sizes of Lithium coin cells is a great help in making up these odd little obsolete battery formats. Long shelf life, high capacity, and i haven't seen one leak yet.

I would think there are more Protimeters out there, but some of them will be rotted out by old batteries of course.

Dave