Avo Valve tester malfunction - UK Vintage Radio Repair and Restoration Discussion Forum

ASH4INFO · 5th Sep 2008, 7:53 pm

I wonder if anyone can give me a start on this problem: my Avo valve tester (model with sloping front controls and valve bases under the top lid) has not been used for some time (couple of years), but now when I switch on the meter needle rises only to the 4 mA mark and can not be adjusted to the right '~' mark, as required prior to doing a valve test.

I notice also something that may be normal, but I cant see why it should be: I checked to see whether the tester was delivering the correct filament/heater voltage to a valve that I wanted to test. So I put my voltmeter (30k ohms/volt) into the two appropriate pin positions on the valve base (without the valve being in place) and was surprised to see a reading of 80 VAC, which stays the same even with the filament switch settings being put back to zero.

Any help much appreciated.

cougar_lou · 8th Sep 2008, 11:05 am

You must give us the Model number in order that we might be able to assist you.

Brian G

XTC · 8th Sep 2008, 11:38 am

Quote:

Originally Posted by ASH4INFO

I notice also something that may be normal, but I cant see why it should be: I checked to see whether the tester was delivering the correct filament/heater voltage to a valve that I wanted to test. So I put my voltmeter (30k ohms/volt) into the two appropriate pin positions on the valve base (without the valve being in place) and was surprised to see a reading of 80 VAC, which stays the same even with the filament switch settings being put back to zero.

30KOhms per volt ( probably 15KOhms per volt on AC ranges) is a very high impedance especially on a range which could measure 80 VAC.

It's possible that this voltage is induced and for some reason the heater circuit is not connected properly. It could be a switch contact, or a loose wire or the transformer.

As Brian says, it's easier to give advice if you can say which model it is.

However, I think it will be a case of getting the circuit diagram and working through the circuit systematically, cleaning switch contacts and checking everything.

Pete.

ASH4INFO · 8th Sep 2008, 11:03 pm

Brian G and Pete - thanks for response. I can find no model number; is there somewhere not obvious I should look. Unfortunately the panel on the back is missing - maybe it would be there? The instruction/operation manual which I think is original with the unit suggests a date of 1952 - perhaps that indicates the model.

Thanks Tony H

XTC · 8th Sep 2008, 11:13 pm

The easiest way is to look at some piccies and decide which yours is closest to.

http://www.duncanamps.com/technical/avotesters.html

It doesn't cover the VCM163, but that one has 2 meters, so is quite distinctive.

Then check the BAMA site to see if you can find the manual. There are other sites but BAMA has a few AVO manuals.

Pete.

ASH4INFO · 10th Sep 2008, 9:00 pm

Pete - thanks for that link. So, its a MK1/2 unit. I wonder if that helps -is this a known failure mode?

Tony H

XTC · 10th Sep 2008, 10:47 pm

Wait and see what others come up with, but I don't think you are going to get a reply along the lines of, "It's obviously component X, which you can replace with RS part 123-4567".

Search this forum site for AVO valve tester problems.

Search the WWW for "AVO valve tester MKII/2".

My googling found this

http://www.jacmusic.com/Tube-testers/index.html

which is very complementary towards the MKII and also includes the operator's manual, as does BAMA. The jacmusic site is very interesting as regards valve testers altogether.

I couldn't find a service manual for the MKII, although I didn't try very hard, but the op manual includes a cct diagram. Maybe the op manual and service manual are combined - I didn't look too closely.

I think you are going to have to do some detective work to track down this fault. However, you said that it hasn't been used for a couple of years. If it's been stored in a garage or loft where it could have become damp, it would be an idea to leave it in an airing cupboard or similar place for a week or so to make sure it's properly dry before further troubleshooting.

Pete.

5th Sep 2008, 7:53 pm	#1
ASH4INFO Retired Dormant Member Join Date: Aug 2008 Location: HONITON Posts: 3	Avo Valve tester malfunction I wonder if anyone can give me a start on this problem: my Avo valve tester (model with sloping front controls and valve bases under the top lid) has not been used for some time (couple of years), but now when I switch on the meter needle rises only to the 4 mA mark and can not be adjusted to the right '~' mark, as required prior to doing a valve test. I notice also something that may be normal, but I cant see why it should be: I checked to see whether the tester was delivering the correct filament/heater voltage to a valve that I wanted to test. So I put my voltmeter (30k ohms/volt) into the two appropriate pin positions on the valve base (without the valve being in place) and was surprised to see a reading of 80 VAC, which stays the same even with the filament switch settings being put back to zero. Any help much appreciated.

8th Sep 2008, 11:05 am	#2
cougar_lou Tetrode Join Date: Dec 2007 Location: Melbourne, Australia Posts: 60	Re: Avo Valve tester malfunction You must give us the Model number in order that we might be able to assist you. Brian G

8th Sep 2008, 11:03 pm	#4
ASH4INFO Retired Dormant Member Join Date: Aug 2008 Location: HONITON Posts: 3	Re: Avo Valve tester malfunction Brian G and Pete - thanks for response. I can find no model number; is there somewhere not obvious I should look. Unfortunately the panel on the back is missing - maybe it would be there? The instruction/operation manual which I think is original with the unit suggests a date of 1952 - perhaps that indicates the model. Thanks Tony H

8th Sep 2008, 11:13 pm	#5
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Avo Valve tester malfunction The easiest way is to look at some piccies and decide which yours is closest to. http://www.duncanamps.com/technical/avotesters.html It doesn't cover the VCM163, but that one has 2 meters, so is quite distinctive. Then check the BAMA site to see if you can find the manual. There are other sites but BAMA has a few AVO manuals. Pete.

10th Sep 2008, 9:00 pm	#6
ASH4INFO Retired Dormant Member Join Date: Aug 2008 Location: HONITON Posts: 3	Re: Avo Valve tester malfunction Pete - thanks for that link. So, its a MK1/2 unit. I wonder if that helps -is this a known failure mode? Tony H

10th Sep 2008, 10:47 pm	#7
XTC Retired Dormant Member Join Date: Oct 2004 Location: Bristol, UK. Posts: 837	Re: Avo Valve tester malfunction Wait and see what others come up with, but I don't think you are going to get a reply along the lines of, "It's obviously component X, which you can replace with RS part 123-4567". Search this forum site for AVO valve tester problems. Search the WWW for "AVO valve tester MKII/2". My googling found this http://www.jacmusic.com/Tube-testers/index.html which is very complementary towards the MKII and also includes the operator's manual, as does BAMA. The jacmusic site is very interesting as regards valve testers altogether. I couldn't find a service manual for the MKII, although I didn't try very hard, but the op manual includes a cct diagram. Maybe the op manual and service manual are combined - I didn't look too closely. I think you are going to have to do some detective work to track down this fault. However, you said that it hasn't been used for a couple of years. If it's been stored in a garage or loft where it could have become damp, it would be an idea to leave it in an airing cupboard or similar place for a week or so to make sure it's properly dry before further troubleshooting. Pete.