Author Topic: AVO VAlve Testers  (Read 6654 times)

Offline charles

AVO VAlve Testers
« on: May 10, 2020, 01:50:38 PM »
AVO Valve testers revisited

Lots have been said about these testers but maybe one has to revive the subject once again because of the revival of valves.

AVO valve testers are very useful instruments because one can test the characteristics of thousands of different valves.  One can even test valves that are not in the respective AVO data manuals by using the specific valve’s data.

It is very useful to match valves regarding the valve’s Emission (Ia) and Mutual Conductance (GM) characteristic’s. It measures amongst others characteristics such as heater/cathode insulation, leakage between the valve elements and gas leakage, hot or cold. It cannot test some transmitter valves that require positive grid voltages. Gm is probably one of the most important characteristic of a valve.

One must ensure that the valve tester is always in calibration because, as for an example, a wrong grid voltage may cause that serviceable valves may measure low emission or vice versa. The other parameters (Va,Vs,Vh, etc) are just as important.

One must be knowable to correct calibrate an AVO valve tester. Measuring the instrument’s grid voltage differ from AVO valve tester models. Some need a link to be removed before measuring and others not.  One cannot just read the grid voltage direct, a conversion factor/s are needed. This is also applicable to Va and Vs readings.   
 
I have most of the AVO models and they differ in their operation from each other. Be careful when operating the tester as one may damage it if not used correctly. There is not a direct replacement for the moving coil meter. Some of the testers do not have a protection circuit for the said meter and it is important to add it in the tester’s circuit. A wrong setting may even cause the burn out of the special grid wire wound potentiometer.   
 
The reason for this short general guideline is because me and a friend restored/repaired/ calibrated a number of AVO valve testers. According to me the CT160 and the VCM 163 are very good valve testers.  The CT160 is the probably the best engineered and build of all the entire AVO valve tester models.

One day I will list in more detail the faults we found in the said testers as well as faulty circuit diagrams. The service manuals are also not so very detailed. 

A last remark, I found some wrong setting in the AVO data manuals but it is a very small percentage when taking in account the thousands of valves listed in the manual.

There will always be some criticism against the AVO valve characteristic testers. My answer, please give a workable alternative solution to test all these parameters of only hundreds and not thousands of valves with say a test jig.  Through the years I tested thousands of valves with my AVO 163 valve tester that saved me a lot of time.  It takes a couple of minutes to check all the relevant valve parameters with an AVO valve characteristic tester.

I would please like some responses from AVO valve tester's users such as Family-Dog and others.

« Last Edit: May 10, 2020, 01:58:38 PM by charles »

Offline Family_Dog

Re: AVO VAlve Testers
« Reply #1 on: May 10, 2020, 03:14:46 PM »
Hi Charles,

Thank you for this, this is something I am definitely looking forward to! I have a few different AVO testers and none of them give exact same results, they will need calibration.

Please go ahead and share as soon as you're ready I will certainly collate and save everything required to calibrate my testers.

-F_D




-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline fredeb

Re: AVO VAlve Testers
« Reply #2 on: May 10, 2020, 06:06:34 PM »
Hi Charles . Thank you for your observations . How does the AVO VCM Mklll rate compared to the other AVO testers ?

Also looking forward to further commentary .

Edit : Could you also please give an example of how one can stuff up that meter , as I'd hate to accidentally do that .  :Ooooooh:



 
« Last Edit: May 10, 2020, 06:21:20 PM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline Des Miles

Re: AVO VAlve Testers
« Reply #3 on: May 10, 2020, 07:00:56 PM »

Hello Charles
This should become an interesting thread. I have a VCM 163 and a "Type 160" which have been sitting, unused, on a shelf for a number of years now. I think this is a good time to get them down and see if they are still in working condition. My only interest is in the restoration of valve radios and I always substitute a suspected faulty valve. I can understand these testers being extremely handy (essential?) for the servicing of high value audio valve amplifiers and for matching of valves, etc.
A quick question, is the Type 160 the same as the CT160 ?
I saw Sputnik, well... actually the booster rocket that went into orbit with it!!

Offline charles

Re: AVO VAlve Testers
« Reply #4 on: May 10, 2020, 08:14:42 PM »
Hi Des,

The VCM 163 is a very sought after valve tester because it is very easy to measure Ia and Gm simultaneously with it.

The 160 and CT 160  is the basically the same instrument. The CT 160 if I remember correctly is the Services model.

In some of the original AVO valve data manuals it is called VT 160 and CT 160 respectively.

fredeb you question regarding the MK III. It is a very difficult one to work on and I would rate it not so high as the other models
such as the Mk IV, 160 and 163.

In short, it is easy to damage the meter with wrong settings.


« Last Edit: May 10, 2020, 08:31:42 PM by charles »

Offline charles

Re: AVO VAlve Testers
« Reply #5 on: May 10, 2020, 08:50:30 PM »
Some other AVO data manuals call it only Type 160.

Offline fredeb

Re: AVO VAlve Testers
« Reply #6 on: May 11, 2020, 02:42:21 AM »
Handy page for AVO aficionados  :  https://frank.pocnet.net/instruments/AVO/index.html
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
Jan Smuts

Offline afroaudio

Re: AVO VAlve Testers
« Reply #7 on: June 15, 2020, 07:18:09 PM »
Interesting discussion, thanks Charles for kicking off... I have a MkIV which has had a diode and cap fitted across the meter to prevent it being damaged. I am guilty of so far not having the time and patience to sit down and get to grips with it. As my work has nearly dried up completely it seems like a good time to do this and I have just hauled the machine upstairs from the garage today for this exact reason.  I will see how I go and post questions here if I get stumped... I would like to test most of my valves over the coming months.

Jonathan

 

Offline Family_Dog

Re: AVO VAlve Testers
« Reply #8 on: June 15, 2020, 08:37:17 PM »
I should run through calibration on mine as well, I have 3 or 4 AVO VCMs and I doubt that any two of them read exactly the same. I also need to catalogue the remainder of my valves, have completed about 60-70% of this so far but it is not the most interesting of tasks to carry out...   :sulky:


-F_D



-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline charles

Re: AVO VAlve Testers
« Reply #9 on: June 15, 2020, 10:23:25 PM »
It is a very good idea to calibrate the AVO VCM's.

I have the same problem regarding the cataloguing of my valves.
One has to do it. A problem may also be storage space.

Offline charles

Re: AVO VAlve Testers
« Reply #10 on: July 29, 2020, 08:40:17 AM »
According to most of the later AVO data manuals:

KT66

Ia = 65mA. This is not correct

Refer to AVO Valve Testing Manual, second edition, 1951

Ia = 85 mA

The KT 66 data sheets also indicates 85 mA

So a measured 65 mA indicates an 76% emission



Offline sercoe

Re: AVO VAlve Testers
« Reply #11 on: August 23, 2020, 12:54:24 AM »
Hi all
As I use a Mk3 and a 160 to test valves, I like both instruments for different reasons. The 160 is portable and very solidly built.  The mk3 has a greater range, eg negative grid volt to about -100V.
Here is a link that describes all the Avos and their weaknesses: https://jacmusic.com/Tube-testers/Analog-Testers-Part1.html
This guy also repairs these fine old instruments.  Even that very rare meter can be repaired apparently.

In future I will use a Roetest as it gives you the option to store all your measurements in a database, characteristic curves included.  :thumbs:

Offline Family_Dog

Re: AVO VAlve Testers
« Reply #12 on: August 23, 2020, 09:44:42 AM »
Very interesting, thank you! I have/had:

AVO Mk1/Mk2  (not working, not sure what happened to it)
AVO Mk3 Still have
AVO Mk4 Still have
AVO VCM 163 Still have
AVO CT-160 (had, swopped it for a Quad II amp with a member here)

The CT-160 meter was blown but I did have it repaired buy am instrument maker from Northcliff, JHB. DOn't know how accurate itwas after that but it did work fine.

-F_D





-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************

Offline charles

Re: AVO VAlve Testers
« Reply #13 on: August 24, 2020, 09:17:08 AM »
The ones I have:

AVO Mk1
AVO Mk2 
AVO Mk3
AVO Mk4
AVO VCM 163
AVO CT-160

Offline Family_Dog

Re: AVO VAlve Testers
« Reply #14 on: August 24, 2020, 11:06:00 AM »
Charles, I thin the two of us are simply "lost cases"... think there's a future for people such as you and I?   :help:


-F_D



-Eric

That Guy in South Africa...
*************************************
http://groups.yahoo.com/group/vintage_tube/
*************************************