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Old 23rd Feb 2023, 12:16 pm   #3141
micheal
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Default Re: AVO Multimeter survey

Hi,

Another DC Avominor for the survey 81463-646 this has the PROPERTY of M.I.M.C. Co LTD. (Marconi International Marine Communication) written on scale plate.
Interesting that Marconi were buying AVO's basic model, comes complete with purpose made leather case with the letters stamped on top.

Mike
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Old 23rd Feb 2023, 3:20 pm   #3142
The Philpott
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Default Re: AVO Multimeter survey

They tend to have MIMCCO on the scale plate as well, no doubt to stop them finding homes outside the business. I think they bought universal avominors as well.

Dave
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Old 8th Mar 2023, 12:50 am   #3143
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Default Re: AVO Multimeter survey

Another one everyone.
Model D : Number 12051-1143
Has a U2 battery fitted that is absolutely rotten!
Came as just the unit, no leads or anything else.
Regards ..... Gary
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Old 8th Mar 2023, 10:44 am   #3144
Phil G4SPZ
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Default Re: AVO Multimeter survey

Good buy. I like the Type D and have a couple. The “div/2” switch is latching which, together with its top DC current range of 15A, gives you a 30 Amp FSD range which is useful for many purposes and unlikely to be found on any other multimeter.
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Old 8th Mar 2023, 11:42 pm   #3145
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Default Re: AVO Multimeter survey

Indeed. Common to see the K button with it's arrow pointing upwards, due to the seller not realising it should be either east or west.

I think i saw this one for sale. Interesting that it doesn't have the AM symbol and crown on the scale plate...and no obvious signs of it having been removed.

This is a great meter when it's working, Gary, it's one of my most used. The downside of it's appeal is that they have been quite heavily used over the years!

Don't try and turn the Q knob, it's a dummy and is glued in. It's a relic of the meter facia having been broadly based on the Model 40/Model 7 types.

Dave
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Old 8th Mar 2023, 11:48 pm   #3146
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Default Re: AVO Multimeter survey

Thanks Phil, nice to hear that. Am I right in thinking the D is pretty well the same as my 48A.
I've removed the battery box, junked the old leaky U2 battery & cleaned the box + parts, so will pop an AA battery holder in place and see what happens with the resistance range.
Then, at some point in the future, I'll get onto cleaning the unit + potentiometers etc.
Regards ..... Gary
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Old 9th Mar 2023, 12:26 am   #3147
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Default Re: AVO Multimeter survey

Similar design philosophy to Model 40/47A/48A series, but the (two) resistance ranges are restricted to quite low values, and the change to a rotary K=1/K=2 range-doubling switch is an advantage as it's hands free unlike the range-halving push button on 40/47A/48A.

Resistance checks are only available on the K=2 setting.

Dave
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Old 9th Mar 2023, 12:27 am   #3148
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by stickfly View Post
Am I right in thinking the D is pretty well the same as my 48A?
Good question… I have a 48A but it’s not easily accessible right now. From memory the 48A is more similar to the Model 40, with its ranges based on a 0-12 scale, whereas the Type D is somewhat different, being based on 0-15 scales. The sensitivities differ too, although none of these is exactly ‘sensitive’. Again, from memory, the Models 40 and 48A have a 2.5mA movement shunted to 5mA (200 OPV) and the Type D has a 3mA FSD movement shunted to 6mA on K=2, so 166 OPV. I can’t remember exactly, but I’m sure someone else will.
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Last edited by Phil G4SPZ; 9th Mar 2023 at 12:36 am. Reason: Clarifications
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Old 9th Mar 2023, 12:43 am   #3149
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Default Re: AVO Multimeter survey

Thanks gents, there seems to be an unbelievable number of different AVO's. Why ?
I wish I'd stuck to just 1 meter, but I can't stop buying them. Blast, just because I was issued one in 1985.
Regards ..... Gary
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Old 9th Mar 2023, 8:04 am   #3150
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Default Re: AVO Multimeter survey

Quote:
Originally Posted by Phil G4SPZ View Post
Quote:
Originally Posted by stickfly View Post
Am I right in thinking the D is pretty well the same as my 48A?
Again, from memory, the Models 40 and 48A have a 2.5mA movement shunted to 5mA (200 OPV) and the Type D has a 3mA FSD movement shunted to 6mA on K=2, so 166 OPV.
Close, but other way round Phil:

The Models 40/47/48 have the 3mA Movement and
the Type D has the 2.5mA Movement.


Ian
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Old 9th Mar 2023, 9:42 am   #3151
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Default Re: AVO Multimeter survey

Thanks, Ian! I stand corrected. No cigar for me…
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Old 9th Mar 2023, 12:09 pm   #3152
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Default Re: AVO Multimeter survey

To add confusion I submitted details to Richard's Radios of a (1947) Model 40 that has a 3.75mA movement shunted to 7.5mA !

It was one of a few specials (probably) made for Lucas Birmingham, having extended ranges and a 150/600 scale instead of 120/480. This is a rather odd spec. since the meters thus became rather similar to a Model D in terms of functionality. Perhaps the Air Ministry had some sort of caveat in their contract, denying supply of clones to outsiders.

400 OPV of the Model D matches that of the Universal Avominor Model 1 and 1A.

I think that ACWEECO may have fallen into the trap of being too helpful and compliant, yet were still successful. They might have flown even higher if they'd restricted their product ranges a little!?.

Dave
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Old 9th Mar 2023, 11:45 pm   #3153
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Default Re: AVO Multimeter survey

Dave, Phil & Ian,
Is there anything you don't know about AVO's ?
This area of the forum should be called "AVOPedia"
Regards ..... Gary
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Old 9th Mar 2023, 11:54 pm   #3154
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Default Re: AVO Multimeter survey

Gary, we’re just PMM’s apprentices. Peter is the real fount of all Avo knowledge!
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Old 10th Mar 2023, 12:44 am   #3155
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Default Re: AVO Multimeter survey

Indeed. The only reason i can be reasonably accurate is that i have only dealt with a small part of the product range! I have nothing after 1968 and very little before WW2.

The inside of a Model D should smell of history, it's only ever tainted if something's got overheated.

Dave
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Old 10th Mar 2023, 4:50 pm   #3156
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Default Re: AVO Multimeter survey

Phil, Dave,

Thank you for your kind words but the real credit should go to the late SPCh who began this thread and was the real brains behind it.

PMM
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Old 11th Mar 2023, 5:00 pm   #3157
stickfly
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Default Re: AVO Multimeter survey

Good afternoon everyone,
I finally got around to cleaning the battery box & fitted an AA holder + battery to the Model D.
There's no resistance at all & the DC seems to be reading very low. A rechargeable C size battery reads 1.28v on my DMM but 0.6v on the D.
OK forget that, I just found the K1/K2 switch

I've now got 2 models to keep me busy
Having a quick look I notice there's a bobbin R that has more modern red/yellow wires fitted, as though it's had problems in the past. The bobbin itself reads OC so there's my starting point. Not today though.
Regards ..... Gary
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Old 11th Mar 2023, 5:57 pm   #3158
Phil G4SPZ
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Default Re: AVO Multimeter survey

Bobbin resistors on Avometers can and do go faulty, but they can be replaced by conventional resistors of the correct value. I have good stocks of resistors of low and odd values, so do drop me a PM if you want anything specific.

A schematic of the Model D is attached. If you can trace the wiring (start at the switch contacts) you can usually identify which resistor is the bobbin. I can't remember as it's been a while since I repaired a Model D.

Phil
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Old 11th Mar 2023, 6:24 pm   #3159
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Default Re: AVO Multimeter survey

Gary,

Your Type D meter has the glass cylinder shunt resistors for two sections of the chain. These use incredibly thin wire and nearly always open-circuit. Judging by what looks like corrosion around yours, I would be surprised if this one is intact.

They can be replaced with conventional high stability resistors mounted on a piece of board (SRBP) or PCB material. I'll look up the values if you need them.

The low sensitivity is a concern. Possibly the magnet has lost field strength, possibly due to previous interference by someone who didn't know what precautions to take. If t his is the case, the 'correct" cute is to remagnetise the magnet but the correct equipment is needed for this. Some people have had success with adding small rare earth magnets.

It's always a good plan to chech the. basic sensitivity of the movement when assessing the condition of a faulty meter.

PMM
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Old 11th Mar 2023, 7:23 pm   #3160
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Default Re: AVO Multimeter survey

For clarification Gary, did operating the K switch solve both problems or did it just activate the resistance range/s?

I have two donor Model D meters easily accessible, if that little bobbin is a standard fitting (rather than a repair from the 'fifties) i should be able to get a value for it tomorrow.

I reckon an AA alkaline should have enough 'thump' for stable operation of the resistance ranges. I have always used C or D alkalines but the latter is definitely overkill (I think it depended on which cell holder i had to hand)

Dave
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