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AVO VAlve Testers

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charles:
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.

Family_Dog:
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

fredeb:
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:



 

Des Miles:

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 ?

charles:
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.


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