AVO Multimeter survey

[The Philpott]

Hi Ian,

Avominors:

The Type H is a 'Universal' Model, ie DCV/DCmA and ACV. It is effectively a Model 1. The only difference i can ascertain is the print on the instruction plate. Type H appears to be the military nomenclature, but not all the Model 1 units issued to the military were badged as Type H.

The Type HR was only issued as a DC (ie DCV/DCuA) model. (As far as we know!)

The Model 1 (U15) series is a basic 400ohm/volt Model 1, but with the 250v range deleted and a 1,500v range added. This may have been due to a request from the military for special uses requiring more than the standard 500v range.

The Model E/Type E is an instrument in it's own right, (800ohm/volt) given ranges to an Air Ministry specification (in the same way as the Model D 'big' Avo ranges were specified.)
The Type E does not have any AC capabilities but it's DC ranges are very useful. Even now it's the weapon of choice for the car glovebox; it's not sensitive enough to be vulnerable to low levels of humidity, and there's no LCD display to deteriorate in the heat.

Dave

[The Philpott]

Avominors:

The Model 1A is a Model 1 with a clever scaleplate. Someone discovered the Model 1 had a Low Resistance Range hidden within it's design. The only extra equipment required was the modified scaleplate and an extra short lead with wander plugs either end. The low resistance range does require all 4 of the wander plugs inserted into the meter to be making very good contact.

The Model 2 Universal Avominor is developed from the Model 1 but is a higher impedance (4kohm/volt) meter.
The movement (if in good condition) has very good damping; better than the Type HR which is 20kohm/volt. I find that occasionally a tap on the meter is required to gain full accuracy; i see this as an unwanted side effect of good damping in a small meter.

Model 2 has a 1mA range in place of the 2.5mA range of the Model 1. This equates to 240mV, for use with external shunts when measuring high DC currents.

Dave

[The Philpott]

Proviso/codicile to Post No. 2301 in this thread, for the uninitiated:

The Type E Avominor and it's stablemates are incompatible with certain modern motor vehicle electronics and can cause damage if used to test sensitive components.

Dave

[Superscope]

Thanks for that pretty good AvoMinor Summary, Dave.
Much appreciated, that is very helpful.

I decided not to collect AvoMinors in an attempt to Limit the
number of Meters in the Collection.
I only have Two.. A Military Model 1 in a Leather Case, which can be repaired, and One for Spares only.
So I know the least about them as a result.

I did get bitten by the MultiMinor though!
So I have a few of those.

Don't know if anybody watches "The Repair Shop", where Vintage
and Antique Items are repaired for their Owners, but their Electrical
Restorer who was repairing an old Radio was actually using a MultiMinor
on his Bench.


Ian

[AndyGilham]

Yes an interesting write up indeed, and pretty much ties in with my list.
Regarding the special U15 variants. From what I have seen, there is no "/" in the name. I have gone with what is on the scale plates which has been U15.xxx-xxx

Andy

[PatMorgan]

AVOMETER 8 mk2 - pencilled on the rear of the glass 141075. Bought of Ebay for £12.68 inc.

Voltage and current ranges apeared ok but resistance didnt work at all- I realised that the upper cam wasnt moving on the rotary switch, so it wasnt going into 'resistance'. i desoldered the shuts to gain access and luckily it was only the cam-screw that had come loose.Fairly clean inside- although some wings off a fly were in there!
The insulator for the heavy shunt/coil had come off- the paxolin and nut/screw were rattling around in the case. Battery terminals perfect.

[The Philpott]

Pat, the cam screw has a crinkle washer under it's head which is normally enough to keep it tight- but every so often one comes loose and then the cam-rotor is free to rotate to any position, as no locating peg is provided..

Sometimes there is no obvious causation, sometimes it occurs because the radial contacts in the meter facia have suffered an arc, and a blob of metal has formed which obstructs rotation of the selector.

That Avo 8 sounds like a good buy.

Dave

[Superscope]

Sorry to drag this back on the AvoMinor Learning Curve!

But what Model of AvoMinor is the one in the Attached Photo?



Also, for those like me who want to know more about AvoMinor's,
from a position of knowing little about them.

Phil started this interesting Thread back in 2013
https://www.vintage-radio.net/forum/...ad.php?t=95556



Ian

[Phil G4SPZ]

Thanks for the reminder, Ian - I’d forgotten how interesting that old thread became! However, that thread covered Universal AvoMinors.

The instrument in your photo is a DC AvoMinor of the earliest pattern, with the straight-sided case and small zeroing knob for the resistance range. I’ve a couple of these, dating from 1934 or thereabouts. There are several variants of the DC AvoMinor and it almost warrants a thread of its own. I bet Dave knows all about them...!

[AndyGilham]

For the DC Avominor, there seems to be 3 variants, based on continual serial numbering.
1. DC Avominor (standard)
2. DC Avominor H
3. DC Avominor HR (High Resistance)

Now the standard model went through a few changes, to the point it almost seems like a mark 2, but the serial number are continuous througout these changes.

The straight side variant was early and seems to have gone to stepped sides between September 1935 and January 1936. Although serial number imply there were 22704 instruments made in that period, which seems very high.

The serial numbers of the two instrument that this change happened are
18251-95 (September 1935) - Not Stepped
40955-16 (January 1936) - Stepped

So my feeling is that when the stepped case was introduced, they started the serial numbering off from 40000, rather than continuing. Which goes again my earlier thoughts!

I am still investigating the socket transition!

Andy

[The Philpott]

I don't know much at all about the basic DC Avominors, they never really sparked my interest! - although i can isolate roughly where the start of the production run was, as i have meter No. 1034-93 from September 1933.

Interesting about the serial number anomaly that Andy mentions.

The facia of the Type HR DC Avominor lacks the upstand/ring around the wander plug sockets- which makes it possible to affect the reading if the end of the operator's finger touches certain unoccupied sockets. I have observed this phenomenon but not investigated whether it's possible to get any sort of electric shock by doing this..others will know.

Dave

[Superscope]

I more confused than ever now!

Just when I thought I was getting my Head round the AvoMinors.

So what Model AvoMinor is the one in the Photo I posted earlier?
Since it seems DC AvoMinors exist in the Model 1 category as well.

Where do we put these earlier incarnations into our Database?
Were they all definitely DC only?

Doesn't seem to be a shortage of these, considering their Age you would think they would be a desired collectible.
Dozens on Ebay all the Time.
Even more unloved than the poor old Model 7 and 40.



Andy

I have changed all the U15 serials to the Format you have observed.



Ian

[The Philpott]

I do not believe DC Avominors were given annotations of Model 1, 2, 3 etc, Ian,

The one you have appears to be No.1. in Andy's list in post No.2310.

Dave

[Superscope]

Dave, Andy, Phil,

Thanks for all the valuable input on this.


Going Forward then, I will record any early DC AvoMinor as "DC AvoMinor"
All other AvoMinor Models will be logged as simply "AvoMinor" (since DC variants or these later Models exist).

So, lets see if I have the basic Story right so far.
As per Phil & Andy's Post #2309 & 2310 there appear to be at least Three Types of the Early DC AvoMinor.

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

Moving onto the Model 1 (Universal AvoMinor), as per Dave's Post #2301 & 2302 we have at least the following Type Variants:
1. Type H
2. Type HR (Actually DC not Universal)
3. Type U15
Plus, one would assume, the Standard version of this Model?

Then we have the Model 1a which I assume at this Stage, has only been identified in a single variant?
For the Model 2, does this later Model have the same Variants as the Model 1 ?

The Model E (A Military DC Instrument not Universal) in a Model 1 Shell.
Has the E been seen in Model 1a or Model 2 guise?

One remaining question I have regarding the Early DC AvoMinor is what is the Stepped Side version?
Anyone have a Photo of One handy?


Ian

[The Philpott]

Hi Ian,
You have Type HR DC under the Model 1 list- this can be deleted as it is already under the DC list. Apart from this it looks good.

You are correct, the Universal Model 1A and Model 2 and Type E don't have any variants as such..All Model 2's (and most Model 1A and some later Type E) will have most of their (voltage range) component resistors on a piggy-back board, which fills up all the available space inside the meter and leaves no room for the leads.

I do have a step-side DC 'minor around which i can photo, i will dig it out. (The smooth side ones were probably found to be too fragile in service) the base of the step-side is wider which gives it much more resilience. Should be a pic on Richards radios somewhere.

I have (mainly) limited my dealings with Avominors to Universals of the period 1945-1957 in order to preserve sanity and leave room in the memory banks for other things!

Dave

[Superscope]

Thanks Dave,

but before I remove the Type HR from the Model 1 list, can I confirm then, that there
is only the One type of HR AvoMinor ?

I thought the Type HR AvoMinor existed in a form of the Model 1 Shell as opposed to the much
earlier square Box style of the original DC AvoMinor?

I have broadly split AvoMinors into Two Physical Groups.

1. Earlier (Some might say uglier) Square Box Style Shell &
2. Later neater and more compact Model 1 Style Shell.


I had managed quite well until recently preserving my Sanity!
At least I know a lot more about them than I did a few Days ago.

I still have no intention of collecting them though, and I plan to off-load the Two I have.




Ian

[micheal]

Hi Ian
There is no DC Avominor type H, as far as I know this designation was only given to
Universal Avominor. Universal meaning AC/DC.

Your picture in post 2038 is DC Avominor early type small ohoms knob and
6V,120V @ 300V voltage ranges.

The only other type of DC Avominor is the type HR ( high resistance 20k/o/p/v)

[The Philpott]

....and, confirmed,there is only the one Type HR Avominor- the DC one. Richard has images of one that i donated a couple of years back.

Now lie back and relax with a damp edition of the Radio Times over your forehead, in the words of a certain Radio 1 DJ from the past!

[The Philpott]

1.Universal Avominor 'U15' scale plate. Note the scale-shape indicator at top left: 'U6'

2. Case was heavily damaged, so movement rebalanced, calibrated and installed in an alternative case, seen measuring mains voltage (error of 5 volts, the rectifier is a little lazy but not enough to persuade me to change it.)

3. DC Avominors for comparison- smooth side and step-side. Note that step-side will not fit in a box designed for smooth side!

Apologies for (rushed) quality of images.

Dave

[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