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Old 31st Jul 2020, 10:17 am   #1
Join Date: Jul 2020
Location: London, UK.
Posts: 1
Default Avo VCM 163, Right hand GM meter fault

Hello All,
I have finally tracked down a 163 in excellent cosmetic condition and made the plunge! Unfortunately it has the standard none working right hand GM meter. I don't have my hands on it at moment, as I need to drive to pick it up, but just looking into my options.
I have read many posts on the forum on this matter and thank all of you who have contributed, I feel confident in turning this unit into a lovely, 100% working and calibrated piece of test equipment with your information and maybe help!
Back to the matter at hand. I note Martins comment on the sticky;

"If you have a hard time finding a replacement meter for the right gm-meter you can use a 100uA meter with an internal resistance of 1500 Ohm in its place if you lower R14 to approximately 90-100 Ohm. This will not affect the measurements, only the current flowing in the amplifier meter circuit to go as high as 100uA through a 1500 Ohm moving coil. A friend of mine have tested this on both frequency response and input signal levels and it works just fine. It night be possible to adjust the feedback loop in the amplifier to suit other meters but I have not done any testing on this"
Could I ask if this is still the preferred method for dealing with a O/C unit, or has someone found a stash of replacement meters! (I know, hens teeth!)

Look forward to your comments

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Old 31st Jul 2020, 11:55 am   #2
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Join Date: May 2009
Location: Linkoping, Sweden
Posts: 1,099
Default Re: Avo VCM 163, Right hand GM meter fault

As far as I know there are no more new meters unfortunately.

So either replacing the whole meter, or just the innards if possible, is right now the only option. There are 50uA movement from Simpson, the Simpson Wide-Vue (1329A or 1329T) series or the True-Vue (TV4TUA050 or TV4DUA050) series that can be used. they are not cheap but very nice meters and I prefer the Taut Band movements as there are no pivots/jewels/hairsprings in those, the 1329T & TV4TUA050.

I am working on a solution with a new replacement meter but Covid-19 has unfortunately delayed it indefinitely so I don't know when I will have time to work on it again. You might have seen this thread here on the forum:
Martin, Sweden
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