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Sets, Parts and Service Information Wanted (private buyers only, no swaps) If you need help obtaining components, sets or equipment, post a message here. Private buyers only - no traders. No swaps.

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Old 16th Nov 2019, 10:41 pm   #1
bud allen
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Default AVO VCM 163 mA/V meter wanted

hello everyone,

I am looking a mA/V meter (or gm meter) for this 163. Sadly Herts no longer repairs them. The coil is open.

If you have one for sale or know of a service that can wind a new coil, please let me know.

I have tried Benchmark Instruments Ltd, and they have a replacement for the other meter.

best greetings
Bud
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Old 16th Nov 2019, 11:32 pm   #2
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Default Re: AVO VCM 163 mA/V meter wanted

What is the specification for the Benchmark meter?

Both meters have identical moving coils at approximately 1500 Ohm at 50uA FSD, but the IA meter has a resistor/NTC temperature compensating network to reach 2400 Ohm at 50uA FSD - maybe you were aware of that already.

So if the Benchmark meter has an internal resistance lower or equal to 1500 Ohm
at 50uA FSD current you can ask if they can provide a temperature compensating network to bring it up to 2400 Ohm.

/Martin
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Old 17th Nov 2019, 12:54 am   #3
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Default Re: AVO VCM 163 mA/V meter wanted

Bud is looking for the Gm meter Martin, so I think he would need to take the thermistor out of the Ia meter if that is what Benchmark are supplying.

I'm pretty sure that I have never heard or seen a meter for a 163 for sale anywhere. My Gm meter is faulty, with some turns shorted, and I have an op-amp in place to compensate for it.

Have you actually taken the movement out of the housing Bud? I once saw a 163 meter which was covered with white crystalline deposits over the small nuts and bolts which pass current through the back of the housing.

B
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Old 17th Nov 2019, 8:47 am   #4
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Default Re: AVO VCM 163 mA/V meter wanted

I forgot to write that "bud allen" could swap the internal meter movements to get a working "gm"-meter and use the Benchmark meter as the IA-meter if it could be adjusted to the correct internal resistance.

/Martin
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Old 17th Nov 2019, 7:05 pm   #5
bud allen
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Default Re: AVO VCM 163 mA/V meter wanted

Quote:
Originally Posted by Bazz4CQJ View Post
Bud is looking for the Gm meter Martin, so I think he would need to take the thermistor out of the Ia meter if that is what Benchmark are supplying.

I'm pretty sure that I have never heard or seen a meter for a 163 for sale anywhere. My Gm meter is faulty, with some turns shorted, and I have an op-amp in place to compensate for it.

Have you actually taken the movement out of the housing Bud? I once saw a 163 meter which was covered with white crystalline deposits over the small nuts and bolts which pass current through the back of the housing.

B
Hi, Thank you for the posts...and Martin too (Martin, I hope you are all well now).

Yes I opened it and the coil is dead. There is no resistor in series or shunt on the coil, a straight/direct terminal to coil. To bad, nice quality construction. I will likely have to find a 20 or 50ua meter that is in the neighborhood of size, etc. and retrofit that into the case. If worse comes to worse, I have two "possible" candidates here. Not what I was looking to do.

I feel kind of bad here, since I told this friend to look out for one to buy, and I would go over it. And there pops up one on eBat. Nice condition and the seller seemed to have "experience' with testers in his feedback. Said it worked and had been calibrated a year or so before. Nope, total lie. Of what I could check out (thanks to Martin who gave me help to redo my own), there is no sign it ever even had any calibration (voltages off by 20%) since the Calibration pot shafts were corroded (no turn marks or mars), no sign it had been ever opened up (all original inside). Buyer beware on Ebay. So if nothing turns up in a few days, I am telling him to seek a refund.

I wrote back to Benchmark on Friday (with a photo) to see what they might have for the mA/V meter (with or without the good/bad card on the knob). We'll see, the other meter was near 250.00usd, and they were very helpful and fast to reply.

Bud
from "on thin ice USA"

Last edited by bud allen; 17th Nov 2019 at 7:11 pm.
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Old 17th Nov 2019, 7:14 pm   #6
bud allen
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Default Re: AVO VCM 163 mA/V meter wanted

Quote:
Originally Posted by Dekatron View Post
What is the specification for the Benchmark meter?

Both meters have identical moving coils at approximately 1500 Ohm at 50uA FSD, but the IA meter has a resistor/NTC temperature compensating network to reach 2400 Ohm at 50uA FSD - maybe you were aware of that already.

So if the Benchmark meter has an internal resistance lower or equal to 1500 Ohm
at 50uA FSD current you can ask if they can provide a temperature compensating network to bring it up to 2400 Ohm.

/Martin
Martin, you are ****** amazing with what you know. You have to be the 5 star member of this site. You have always helped me understand this machine, and without you... I never would have. So Thank you !!!
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Old 18th Nov 2019, 5:54 pm   #7
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Default Re: AVO VCM 163 mA/V meter wanted

Thanks, I try to help where I can.

I am right now working on a replacement meter for both the Ia- and gm-meters for the VCM163, I have some more things to do to finish those before I can publish them however.

I just keep my fingers crossed that the Swedish Postal service doesn't loose more of my parcels, but you never know, they are at an all time low when it comes to bad service...
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Old 18th Nov 2019, 8:24 pm   #8
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Default Re: AVO VCM 163 mA/V meter wanted

A picture would help those of not familiar with the test gear in question.

Andy.
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Old 18th Nov 2019, 9:22 pm   #9
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Default Re: AVO VCM 163 mA/V meter wanted

Quote:
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A picture would help those of not familiar with the test gear in question.Andy.
A moment on Google will bring you back to this Forum - see post 11https://www.vintage-radio.net/forum/...ad.php?t=35564
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Old 18th Nov 2019, 11:55 pm   #10
bud allen
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Default Re: AVO VCM 163 mA/V meter wanted

Photo of the inside of the AVO VCM163 mA/V meter or gm meter.

Simple, no resistor in series or shunt.
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Old 19th Nov 2019, 7:44 am   #11
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Default Re: AVO VCM 163 mA/V meter wanted

Thanks Bazz, sorry, was being lazy. From that thread it seems the OP might have some meters and is still an active member, might be worth dropping them a PM. I'll have a look in my stash but they look pretty cheap movements.

Andy
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Old 19th Nov 2019, 4:17 pm   #12
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Default Re: AVO VCM 163 mA/V meter wanted

A possible alternative is the Skywood 500 analogue multimeter, that is 30,000 ohms/volt so 33uA.

A conversion chart from the VCM meter to the MM volts scale will get you working, mirror scale as well.

I was amazed the 15V battery still produced FSD on the ohms range, no AA cell for the lower ranges.

Could just use a DC millivoltmeter with the same conversion chart.
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