AVO VCM meter substitute? - UK Vintage Radio Repair and Restoration Discussion Forum

woodchips · 21st Apr 2011, 10:07 am

Hello, been reading about the problems with the very sensitive meters used in some of the AVO VCMs.

I was just measuring some AC millivolts with a HP3400 true RMS analogue meter when I noticed it had a DC output jack on the back. Being true RMS then could this be used in place of the standard meter, with the DC output driving something a little less fragile than a 33uA meter?

Just a thought, the 3400 isn't very expensive now. My AVO is a Mk1 so has the 1mA meter movement.

Bob

Dekatron · 21st Apr 2011, 11:12 am

As long as you load the VCM with the correct resistance of 3250 Ohm for the Mk III, mk IV and CT160 or CT160A it is ok to use a high impedance meter connected across that resistor to make the measurements. You can even use a small DMM module if you wish, you will just have to know what each value corresponds to on the different scales or make a switch that selects the range for each scale. This has been done by JacMusic on his Valve Tester webpage: http://www.jacmusic.com/Tube-testers...ital/index.htm

woodchips · 23rd Apr 2011, 11:37 am

Perhaps I was a bit too economical with the words.

Obviously a DVM or similar meter can replace the VCM meter, but I was thinking here about transferring the scale from the dead original meter into a more easily obtained replacement. This keeps the looks of the VCM the same. Possibly the greater benefit is that the overload protection has now been transferred to the HP3400, and it doesn't matter what the fault is you are not going to blow it up. Replacing with another sensitive meter does not have this advantage, it is also probably quite a bit more expensive.

Bob

zooterman · 24th Apr 2011, 2:41 pm

A company called Benchmark in Ludlow, Shropshire, tell me that they have a meter suitable for Avo.
contact at lorraine@benchmark-bpl.com

Dekatron · 24th Apr 2011, 3:20 pm

I tried to order just one meter over a year ago, to make some tests with, from Benchmark but they kindly told me that they had a minimum amount that I needed to order. If anyone contacts them again and they can sell the meters one by one I would be glad if you could inform me, I'd buy one immediately.

I ended up using Simpson 29T taut Band meters instead, as you can read more about here on the forum: https://www.vintage-radio.net/forum/...ad.php?t=68395

einovaan · 24th Apr 2011, 4:22 pm

I have ordered many years ago a meter from England. Its size is 120 mm x 97 mm. There reads on its side: SIFAM, Made in England, 30 uA, RES 3250R NOM. It was quite expensive and I have not used it yet.

DaveH-UK · 2nd Oct 2012, 9:40 pm

This looks like an answer to a virgin's prayer.

I see that no one has commented on this so far (from what I can find), would not this meter act as a replacement for an AVO VCM meter (30uA). I see that their current range is with 50uA movement.

http://www.sifam.com/meterCategory.asp?cat=Presentor - Industrial

I have not searched other meter manufacturers and perhaps others have tried, but surely 30uA meters must be available from somewhere for those that are unfortunate to have dud meters in their testers?

Thankfully, mine is still ok at the moment. I have everything crossed, but who knows when it might fail.
DaveH-UK

DaveH-UK · 2nd Oct 2012, 11:56 pm

Aghhh, looks like I should have dug a bit deeper before I posted the above. It looks like Martin is already on the case with the Simpsons meters as a substitute. I will go back and follow the thread

.

alexander-fa · 6th Nov 2013, 6:20 pm

Quote:

Originally Posted by einovaan

I have ordered many years ago a meter from England. Its size is 120 mm x 97 mm. There reads on its side: SIFAM, Made in England, 30 uA, RES 3250R NOM. It was quite expensive and I have not used it yet.

I am looking also to find a replacement meter for my AVO VCM MK4
Could you please inform me where you bought this meter from?
Sifam doesn't answer to my messages and a distributor told me, this meter is out of production from 2009

21st Apr 2011, 10:07 am	#1
woodchips Octode Join Date: May 2010 Location: Grantham, Lincolnshire, UK. Posts: 1,174	AVO VCM meter substitute? Hello, been reading about the problems with the very sensitive meters used in some of the AVO VCMs. I was just measuring some AC millivolts with a HP3400 true RMS analogue meter when I noticed it had a DC output jack on the back. Being true RMS then could this be used in place of the standard meter, with the DC output driving something a little less fragile than a 33uA meter? Just a thought, the 3400 isn't very expensive now. My AVO is a Mk1 so has the 1mA meter movement. Bob

21st Apr 2011, 11:12 am	#2
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: AVO VCM meter substitute? As long as you load the VCM with the correct resistance of 3250 Ohm for the Mk III, mk IV and CT160 or CT160A it is ok to use a high impedance meter connected across that resistor to make the measurements. You can even use a small DMM module if you wish, you will just have to know what each value corresponds to on the different scales or make a switch that selects the range for each scale. This has been done by JacMusic on his Valve Tester webpage: http://www.jacmusic.com/Tube-testers...ital/index.htm __________________ Martin, Sweden

23rd Apr 2011, 11:37 am	#3
woodchips Octode Join Date: May 2010 Location: Grantham, Lincolnshire, UK. Posts: 1,174	Re: AVO VCM meter substitute? Perhaps I was a bit too economical with the words. Obviously a DVM or similar meter can replace the VCM meter, but I was thinking here about transferring the scale from the dead original meter into a more easily obtained replacement. This keeps the looks of the VCM the same. Possibly the greater benefit is that the overload protection has now been transferred to the HP3400, and it doesn't matter what the fault is you are not going to blow it up. Replacing with another sensitive meter does not have this advantage, it is also probably quite a bit more expensive. Bob

24th Apr 2011, 2:41 pm	#4
zooterman Retired Dormant Member Join Date: Jan 2007 Location: Lampeter, Dyfed, Wales, UK. Posts: 369	Re: AVO VCM meter substitute? A company called Benchmark in Ludlow, Shropshire, tell me that they have a meter suitable for Avo. contact at lorraine@benchmark-bpl.com Attached Thumbnails

24th Apr 2011, 3:20 pm	#5
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: AVO VCM meter substitute? I tried to order just one meter over a year ago, to make some tests with, from Benchmark but they kindly told me that they had a minimum amount that I needed to order. If anyone contacts them again and they can sell the meters one by one I would be glad if you could inform me, I'd buy one immediately. I ended up using Simpson 29T taut Band meters instead, as you can read more about here on the forum: https://www.vintage-radio.net/forum/...ad.php?t=68395 __________________ Martin, Sweden

24th Apr 2011, 4:22 pm	#6
einovaan Retired Dormant Member Join Date: Jan 2011 Location: Oulu, Finland. Posts: 65	Re: AVO VCM meter substitute? I have ordered many years ago a meter from England. Its size is 120 mm x 97 mm. There reads on its side: SIFAM, Made in England, 30 uA, RES 3250R NOM. It was quite expensive and I have not used it yet. Attached Thumbnails

2nd Oct 2012, 9:40 pm	#7
DaveH-UK Retired Dormant Member Join Date: Sep 2012 Location: Winchester, UK Posts: 36	Re: AVO VCM meter substitute? This looks like an answer to a virgin's prayer. I see that no one has commented on this so far (from what I can find), would not this meter act as a replacement for an AVO VCM meter (30uA). I see that their current range is with 50uA movement. http://www.sifam.com/meterCategory.asp?cat=Presentor - Industrial I have not searched other meter manufacturers and perhaps others have tried, but surely 30uA meters must be available from somewhere for those that are unfortunate to have dud meters in their testers? Thankfully, mine is still ok at the moment. I have everything crossed, but who knows when it might fail. DaveH-UK

2nd Oct 2012, 11:56 pm	#8
DaveH-UK Retired Dormant Member Join Date: Sep 2012 Location: Winchester, UK Posts: 36	Re: AVO VCM meter substitute? Aghhh, looks like I should have dug a bit deeper before I posted the above. It looks like Martin is already on the case with the Simpsons meters as a substitute. I will go back and follow the thread .