AVO Model 9 Mk IV variation

[Superscope]

I have a Model 9 Mk IV where the Main Board appears to be very different from the usual Mk IV board.

Instead of the V shaped cut-out which gives access to the Meter Movement, this one has a square shaped board which covers the entire Meter Movement, with just a square hole in the middle allowing the Meter Movement Magnets to stick through.

The board also very clearly has printed tracks on the underside unlike the normal Mk IV board.

Ian

[pmmunro]

Ian,

This would probably be best to be a separate thread so that it can be found more easily for future reference.

This does appear to be an unusual form of construction. Could you possibly show a few photographs please?

PMM

[Superscope]

Please see Photos attached.

The Model 8 Mk IV is on the left in both Pictures.
The Model 9 Mk IV is on the right in both Pictures.

The Model 9 has a 1969 date, a standard Mk IV Case and the older style Cut Out.
The Case is undamaged, no cracks at all, but the Panel was/is a very tight fit.

The Model 8 unfortunately has no Date. Not sure if the Movement has been replaced,
but it does have a Mk V style case. It has the Newer style Cut Out introduced for the Mk IV.

[Sinewave]

Come the 8 Mk 4, there was a shift from putting dates in the movement to using a label on the side of the case with the serial number and date. Sometimes for some reason some meters have missing labels.

[Superscope]

I guess it would be interesting to hear from anybody with a Mk IV normal style
case to see if any of them have the later Label type serial No and no serial on the
Meter Movement.

My 8 Mk IV has the Mk V Style case, but it has Mk IV data plate.
So it is correct for the Meter.

So either this was original to the Meter when New, or as PMM mentioned, it was
probably a replacement made for the Mk IV due to the problems with
the cracking of the original Plastic Cases.

Seems odd though, that the Serial is missing from the Movement. This would suggest
that either the Meter Movement has been replaced as well, or it always had a Label type
Serial No.

Ian

[Sinewave]

My mark 4 (normal case) has the later type label.

Sounds normal. They stopped putting serials in the movement come the Mark 4 when they went to the label format.

[Superscope]

You learn something everyday!

Didn't know the Labels started during Mk IV production.

How about the interior layout of your Mk IV?
Have you seen the Circuit Board Layout of the 9 Mk IV in my Photo
before?
I've not seen this arrangement before.


Ian

[Sinewave]

I've never opened my 9 Mk 4.

My 8 Mk 4 looks like yours does.

[pmmunro]

Ian,

I've never seen the printed circuit version as in your Model 9 Mark IV before. The earliest Mk IV meter which I have is dated June 1970 and the Model 8 Mark V was introduced in December 1972, replacing all previous versions of Models 8 and 9.

According to a former production manager at AVO, the Model 8/9 Mark IV was an attempt to reduce production costs, especially assembly times. The MK V versions must have needed a long development time, especially as they were intended to meet NATO specifications from the start, so the Mk IV is likely to have been in production during the Mk V development time. It would seem unlikely that any further development time would have been devoted to the Mk IV once the decision on Mk V development had been taken.

Discounting the possibility that your PCB Mk IV was made by anyone other than AVO, it leaves the possibility that it was an early prototype whose design was rejected in favour of the more conventional and familiar construction.

Any information on your PCB Mk IV's provenance would be of great interest. I wouldn't have thought it could have got out of the factory unofficially if security at Dover was as tight as I have been told it was at Vauxhall Bride Road.

PMM

[Refugee]

You are tempting me to have a look in my two 9 MK IVs to see what style of construction they are. The outer cases are slightly different and they also have there first owners name on the front panels.
They were bought from a factory closure sale by the previous owner to me.

[Superscope]

Well it would be interesting to see how many off these types of Mk IV's are out there!
Maybe we can build up a picture of when these were built.
Could be Model 8's as well, who knows.

The Serial on mine is: 1424-IV-969
Last Calibrated in Jan 1983
I guess this makes it an early-ish one, not sure the exact Date Mk IV's were released.

It also has a Black Plastic Case, rather than the Green Plastic.
Connection to the Panel is via Spikes on the PCB and Sprung Metal contacts as per
the original style Model 8 and 9's, although different materials have been used.
Not the Flying Leads found on the normal Mk IV's.

I do not own a Mk IV with the Green Case, so I have nothing to compare the
Black Case with, but it seems quite robust, so maybe why this one hasn't cracked.

It is 3mm thick along the side, 4.2mm around the Rim.

It still has a number of EMI labels attached, so I guess they were probably the First
owners.


Ian

[dolphin]

Some years ago I was given a Model 9 Mk IV. The serial on the dial is 1237-769.

Recently the glass became detached and I too found the front panel was a very tight fit (which is why I haven't removed it again to take a photo!)

The construction looks very much like Ian's photos and because of the way the PCB covers the meter movement it looked impossible to fix the loose glass without dismantling the whole thing. Disappointingly I had to resort to improvising with blobs from a glue gun and hastily re-assembled the darn thing!

Max

[philthespark]

I was speaking to one of the old boys from Megger Instruments last year at an industry event,as some of you will know, AVO at one point became part of Megger, and he was saying that they were in the process of setting up some sort of museum of old test equipment, whether it was going to be public, or just for those working within the industry was unclear, however he certainly knew a lot about the older kit, perhaps it would be worth giving them a ring and seeing if they can shed any light on this unusual meter design.

[Superscope]

Max,

Maybe we are narrowing it down already.
Not sure when the Mk IV was launched, but I'm guessing 1969.

It would appear at the moment then, the first Mk IV's had this Repair Unfriendly
design. Bit too early to make a definitive conclusion though.

We just need to hear from a few more Mk IV owners (Model 8 and 9's) to find the
cut-over Date.

Unfortunately for me, mine needs to be disassembled due to a faulty Rev MC switch.
Only get readings with the Rev MC switch depressed. Nothing in the normal position.

But it has to wait until my Model 8 is repaired, hence the removed Transformer Board
in my earlier Photos.

Still ,that's part of the Fun.

Ian

[Superscope]

Hi Chaps,

It has gone a bit quiet, so I would like to put the call out to all
Model 8 or 9 Mk IV owners who happen to have their Meters open,
or are brave enough just to take a look inside, if they could post their
serial Numbers together with the extra information on the Style of the
Main Board (V Cut out, or Square) and also the colour and style of
the Case.

Case Styles I know about are:
Green with known problems of cracking
Black
Mk V style Case maybe replacement Original?


Ian

[Superscope]

I "bit the bullet" in my Mk IV research and picked up another one to have
a look inside.

This was an 8 Mk IV with the Black Plastic Mk IV style Case. Again, as I have
found previously, the Case is free of any cracking, unlike the common
problem of the Green Case. Serial is printed on the Scaleplate.
I was hoping that it would also have the Repair Unfriendly PCB, so I
could associate the Black Case with the Square Meter Movement Cut Out.

Unfortunately not!
This Jan 1970 Meter has the Standard V Cut Out Mk IV Board.
So there would appear to be no correlation between Case and Board Style!

So I wonder:
What Date did the change to the V Cut Out happen?
(The Square Cut Out seems to be the early Mk IV's). and

What Date did the Green Case replaced the Black Case?
(Assuming that happened in any logical order of course, and did
the Green or Black come first?)

Another thing I noticed, all the Model 8's (Mk IV) I've seen, have the "8 IV"
printed on the Scaleplate, regardless of whether the Serial number is printed there or not.

I have not yet seen a Model 9 Mk IV with a "9 IV" printed on the Scaleplate



Ian

[Chris_A]

I've got a few, I'll try and have a look over this weekend or over the bank holiday weekend.

Chris

[Chris_A]

Ian,

I have dug a few out to look at, I think that I have a couple more, one of them I think has a Mk5 case, I'll try and find them later, I'll add all details to the survey pages later.
#1
A model 8 Mk4, its marked 8 IV on the dial, Ser No. 65500 84/3/72.
The label is missing from the side of the case. The Ser No is engraved on the case but there is a secondary label behind the battery back plate.
Its in a standard Mk4 style grey plastic case (I think that its some sort of oxidization that gives it a green tinge).

[Chris_A]

#2
A model 8 Mk4, the Ser No. 5784 . 1164 is marked on the dial.
Its in a standard Mk4 style grey plastic case, no case markings
Last Cal Feb 2003.

Chris

[Chris_A]

#3
A model 9 Mk4, its marked 9 IV (printed) on the dial.
Ser No. 63202 94/1/72 is on the case label.
There is no secondary label behind the battery back plate.
Its in a standard Mk4 style grey plastic case.