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Old 21st May 2018, 3:13 pm   #21
Chris_A
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Default Re: AVO Model 9 Mk IV variation

#4
A model 9 Mk4, its marked 9 . l V. (Handwritten) on the dial.
Ser No. 77758 94/10/72 is on the case label.
There is no secondary label behind the battery back plate.
Its in a standard Mk4 style grey plastic case.
Last Cal Apr 82.
This case has 7 screws (most of the other Mk4's have 6!!!).
There seems to be some build differences on this one

Chris
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Old 21st May 2018, 3:44 pm   #22
Chris_A
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Default Re: AVO Model 9 Mk IV variation

#5
A model 8 Mk4, its marked 8 IV (printed) on the dial.
Some difficulty reading the label and the format seems strange, I've attached a picture to see if anyone can make sense or recognise the format.
As far as I can tell Ser No. *3077 524/ 170 is on the case label, the first digit could be a 0 or 8, I guess it may also be a 6 which may make more sense, can anyone help?
There is no secondary label behind the battery back plate.
Its in a black Mk4 style plastic case similar in style to the grey cases.
This case also has 7 screws.

I hope the info and pictures have helped.

Chris
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Old 21st May 2018, 3:50 pm   #23
Sinewave
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Default Re: AVO Model 9 Mk IV variation

The 170 is likely to mean Jan 1970 as the date of the meter.
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Old 21st May 2018, 3:58 pm   #24
Chris_A
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Default Re: AVO Model 9 Mk IV variation

Probably, its just the format that seems a bit strange

Chris
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Old 21st May 2018, 4:01 pm   #25
Sinewave
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Default Re: AVO Model 9 Mk IV variation

They did undergo a few format changes.

When the Mark 5 was launched, on the date part of the label they started a new format which would say 8V/Month/Year.

I took me a while to work out the 8V meant Model 8 mark 5
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Old 21st May 2018, 4:46 pm   #26
Chris_A
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Default Re: AVO Model 9 Mk IV variation

yes and all the ones in that format style (starting 84 or 94) are all dated later so this one must have been in a transition time when they were trying to figure a new format style.
Does anyone know when the Mk4's were introduced as #2 with the Ser No date of 1164 seems early.

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Old 22nd May 2018, 12:07 am   #27
Superscope
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Default Re: AVO Model 9 Mk IV variation

Chris,

Thanks for the comprehensive update from your Mk IV collection.
All yours seem to have the standard V cut out Board.

So far, it looks like the Square Cut Out Repair unfriendly PCB is a
1969 or earlier design, but still a bit to early to make a definative
conclusion.

No conclusions at all yet on the Case colour. Two of my Mk IV's are definitely Black, not Grey or Green. They are 1969 and 1970 vintage, so it's
leaning towards the Black case being an earlier design, but again, not enough info yet for a definitive conclusion on that either.

No conclusion yet either, as to when the Serial Number changed from
a printed Scaleplate to a Sticky Label.

Not sure what Date your #2 is, 1964 is to early for a Mk IV.

I happened across a posting on the AVO Multimeter Survey (# 200)
which you have just confirmed, in that Model 9 Mk IV's do exist with
the 9 Mk IV printed on the Scaleplate similar to Model 8's. Although,
for some reason I think this is rare on a Model 9. I have never even
seen a picture of a 9 with this printing, but all Model 8 Mk IV's seem to have it. But you are the second person who appears to have the Printing on their
Model 9.


Ian
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Old 22nd May 2018, 12:21 am   #28
Refugee
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Default Re: AVO Model 9 Mk IV variation

Post 820 in the survey.
I never opened either of the meters up and only looked for a serial number on the scale plates.
One must have been on the scale plate.
Perhaps I aught to have a closer look some time.
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Old 22nd May 2018, 1:03 am   #29
Sinewave
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Default Re: AVO Model 9 Mk IV variation

Quote:
Originally Posted by Superscope View Post
I happened across a posting on the AVO Multimeter Survey (# 200)
which you have just confirmed, in that Model 9 Mk IV's do exist with
the 9 Mk IV printed on the Scaleplate similar to Model 8's. Although,
for some reason I think this is rare on a Model 9. I have never even
seen a picture of a 9 with this printing, but all Model 8 Mk IV's seem to have it. But you are the second person who appears to have the Printing on their
Model 9.
All of my (which is three or four units I think) 9 Mk IVs have "9 IV" on the scaleplate, but the serial is a sticker on the side.

My 9 IIs have only the serial in the scale.
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Old 22nd May 2018, 9:50 am   #30
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Default Re: AVO Model 9 Mk IV variation

Chris,

Your #2 meter, Ser No. 5784 . 1164 is almost certainly a hybrid with a Model 9 Mk II scaleplate. The date is very firmly in the Model 9 Mk II or Model 8 Mk III era which is confirmed by the mirror. In this meter, the mirror is an arc slightly wider than the curved slot in the scaleplate, in all your other Mk IV meters the mirror is a large rectangle held in place by tape similar in appearance to masking tape.

I don't think it is a complete movement swap because otherwise the movement seems to be a Mk IV type with the swamp adjusting pot. The attachment is a photograph of the rear of a Model 8 Mk III movement; a Model 9 Mk II would look very similar.

Quite why anyone would change just a scaleplate is open to question. Scaleplates should be matched to the movement they are used with. Up to the middle 1960s this was done by individual hand calibration, later by selecting scaleplates for "scaleshape" from a range of 12 different types. The scaleshape type number is marked at the bottom centre of the scaleplate. Interchanging scaleplates is very likely to compromise the accuracy of the meter over some part of the scale.

The attachment of the mirror of your 5784 . 1164 appears to be by PVC insulating tape which does not suggest a professional repair.

Until this thread, the best information I could find suggested that Mk IV production started around late 1969/early 1970, but this would suggest that it could have been earlier in 1969.

PMM
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Old 22nd May 2018, 7:52 pm   #31
Chris_A
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Default Re: AVO Model 9 Mk IV variation

Hi PMM,

I've just had another look I think that you're right. It looks possible that for some reason the scaleplate has been replaced with one possibly recovered from an older meter.
My 9 Mk2 has the newer scaleplate with the mirror further up the scale and the resistance range at he bottom but the scaleplate looks like an 8 Mk3, were earlier 9 Mk2's the same, I've added a couple of pictures of the scale.

Chris
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Old 22nd May 2018, 7:56 pm   #32
Chris_A
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Default Re: AVO Model 9 Mk IV variation

Ian,

I've added a couple of pictures of the 9 Mk4 scaleplate markings, one printed and one handwritten

Chris
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