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Old 18th Aug 2019, 7:55 pm   #1
sven_swe
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Default AVO CT160 Meter Replacement - Done!

Hi all,

Just wanted to share my story about refurbishing and fitting a new meter in my CT160 (and MK3 ongoing). Since my meter to my AVO CT160 VCM was "lost" in transit by a big German shipping provider on the way to be serviced in England by Herts meter, I had to find a replacement meter.
For my AVO Mk3 VCM it's a different story, the original meter was described as "pivoty" after service, it sometimes gets stuck and needs a slight tap to go back to zero. This is phenomena is especially occurring in the mounting angle of 60 degrees in the MK3. When being vertical or horizontally mounted it works better. I do not have spare parts to mount new jewels.

It's almost impossible to find a single meter unit but after some reading on this forum I found that Dekatron (Martin, Sweden) might have a solution. I got in touch with him and asked for his help. Discussing the issue with him was great and he designed a solution. The new meter from Martin also has the "dampening" protection unit built-in on the PCB behind the meter, which is easily mounted with the existing screws.
Thanks to Martin I now have a fully working and very accurate CT160 again!

Since the design is a little bit different of the meter compared to the original, which has a cut-out to let the "overload" lamp red light come through, there are Plexiglas plates with LED mounted in them and driven from a separate unit, very easy to connect only with cables to the relay, mains and the LED. It works perfect and it lights up red very strong, it can't be missed.

After some tweaking and replacing the calibration resistors that had drifted, 8uF elko change, and change of some other misc components the voltages are now within spec.

David Simpson was also very helpful in providing me with a "standardized valve" for comparison with his machine. I also made a standardized ECC82 according to the instructions in the service manual for my own comparison and it is very accurate.

Please see pictures of the mounted PCB̈́'s and installation of the new meter from Martin.

Thanks to everyone else for also helping with some questions I've had. This is a clear upgrade from the original meter in my opinion.

Btw, does anyone know why the machine smells so good?
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Old 18th Aug 2019, 8:59 pm   #2
David Simpson
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Default Re: AVO CT160 Meter Replacement - Done!

Marcus - you've done a great job. You're a credit to the valve tester/valve testing fraternity. And great Ia/Vg graph results.
Mycket god arbete, min ven.

Regards, David
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Old 19th Aug 2019, 8:30 am   #3
Sinewave
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Default Re: AVO CT160 Meter Replacement - Done!

Your meter movement disappeared from the entire valve tester whilst in transit?
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Old 19th Aug 2019, 10:42 am   #4
Herald1360
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Default Re: AVO CT160 Meter Replacement - Done!

No, just the meter itself whilst in transit to a meter repairer.
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Old 19th Aug 2019, 10:49 am   #5
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Default Re: AVO CT160 Meter Replacement - Done!

It would have been slightly worse if it'd disappeared on the way back, I suppose.

The finished VCM160 looks fine. Good work!

And the meter is now a lot less fragile than the original.

David
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Old 19th Aug 2019, 11:31 am   #6
sven_swe
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Default Re: AVO CT160 Meter Replacement - Done!

Quote:
Originally Posted by David Simpson View Post
Marcus - you've done a great job. You're a credit to the valve tester/valve testing fraternity. And great Ia/Vg graph results.
Mycket god arbete, min ven.
Regards, David
Tack så mycket David! But I was merely the "tester" in all this, it's all Martin's design

Thanks again for the valve! It will be available for others when I'm done with my MK3, just let me know.
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Old 19th Aug 2019, 11:33 am   #7
sven_swe
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Default Re: AVO CT160 Meter Replacement - Done!

Hi,

Yes it was only the meter that got lost. Yes on the way back would have been awful!

David, yes I agree, it's less fragile and has a very nice movement. It's a pleasure to use it.
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