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Old 14th Apr 2024, 7:24 pm   #1
RichardGM
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Default AVO Model 7, serial no. 22706

I collected this the other day from a friend (not the same friend whose late husband's stuff I have been offering here from time to time). It had belonged to this friend's late husband and has evidently had a hard time, possibly before he acquired it.

The two screws that should hold the battery cover on through keyhole slots had both been replaced by woodscrews forced into the holes. All the screws that should hold the back of the case on were missing. One had been replaced by a 4 BA screw which had threaded itself into the hole in the case and pushed that out from the body of the meter. A 6 BA screw almost fits but not quite. What should these screws be?

Can someone explain the rotating butterfly(?) clip on the battery cover?

Inside, a little daughter board has a bracket that evidently should be fixed to the main board but is hanging loose, supported only by its wires, and there is one green wirewound resistor that doesn't look original.

I have done a quick calibration check on a few DC voltage and current ranges. It is reading 10% to 20% low except on the 10 V range where it is bang on. I am wondering whether that green resistor was added to correct the calibration on that one range.

What do people think? Does this deserve a full overhaul or should it just go into someone's collection as it is?
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Old 14th Apr 2024, 7:28 pm   #2
RichardGM
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Default Re: AVO Model 7, serial no. 22706

I thought I had uploaded a picture of the front. I'm trying again.
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Old 14th Apr 2024, 10:31 pm   #3
The Philpott
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Default Re: AVO Model 7, serial no. 22706

Would be interesting to know what ASRE stands for in the military.

The rotating clip is to secure the probes that (would have) sat in the recesses.

I think the casing screws should be 6BA (anyone?)

Before deciding the meter calibration is wrong, check that the Q button is behaving correctly insofar as it's 'lift and turn' movements and the associated contacts are concerned. It's a clever device, but prone to play up in old age. It plays havoc if it's not making proper contact. (Normal readings are taken with Q fully anticlockwise and home in the meter facia, as per the instructions)

Best to assess this before it passes to a new owner, i suppose...although people do like puzzles.

Dave
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Old 15th Apr 2024, 12:18 pm   #4
RichardGM
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Default Re: AVO Model 7, serial no. 22706

Thanks, Dave, for that info.

I didn't have the instructions but have now downloaded them.

I've tried again with 6 BA screws in several of the holes. They go in about three turns then won't go any further. Would the originals have been very short, not needing to go more than three turns?

The Q knob is indeed fully anticlockwise. I've now checked the 1 V range and that is also bang on. If the Q pot was playing up I would expect it to affect all ranges equally.

I don't think I can justify the time to find my way round the circuit and work out what needs to be changed to correct the calibration. A quick eBay search shows many Model 7s for sale at modest prices, so I'm inclined to offer this one FOC, if my friend agrees.
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Old 15th Apr 2024, 1:40 pm   #5
The Philpott
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Default Re: AVO Model 7, serial no. 22706

Yes, they're not rare but they're comparatively tough.

I think the last time Q was giving me problems i diagnosed it by lifting it out of the panel and letting it snap back into place- the silver/gold arrowhead contact in the end of the prod had actually come loose.

With meters having a metal case rather than bakelite, the casing screws are extremely short.. thus when a safety flash test is performed they don't cause a fail.

Just checked an aluminium cased Model 7, screws go in by around 6.5 full turns, overall length of screw 1/4". Sounds like your threads have been chewed up.

There's at least one member here who very much likes the Model 7, i have two already so that's adequate!

Dave

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Old 15th Apr 2024, 2:10 pm   #6
Andrew Sinclair
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Default Re: AVO Model 7, serial no. 22706

ASRE is the Admiralty Signals and Radar Establishment

The navy signal school was moved from Portsmouth to Haslemere in WWII due to the threat of bombing and was re-named ASRE. It is the descendant of one of the earliest radio establishments in the world.
https://en.wikipedia.org/wiki/Admira..._Establishment

This AVO 7 certainly has a history.!
Andrew
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Old 16th Apr 2024, 10:50 pm   #7
Graham G3ZVT
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Default Re: AVO Model 7, serial no. 22706

In case you are wondering...
...see highlighted text.
http://www.portsdown-tunnels.org.uk/...ious%20reasons.
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