Avo Valve Tester

[Sparks]

Thanks, I didn't know that. I can't see a link to the manual!
Bob

[pwdrive]

Thanks, I didn't know that.   I can't see a link to the manual!
Bob

Bugger.....'ere 'tis:

http://www.jacmusic.com/Tube-testers/AVO/avovalve.pdf

Also in the website section of the forum

Lawrence.

[kalee99]

Hi,
I have the two panel tester but mine has the thumbwheel selectors on the valve panel. As far as I understand it the thumbwheel unit was an upgrade and could be added at anytime to the meter unit as a direct replacement. The thumbwheel panels often turn up on their own on the internet auction sites. So it would be worth looking out for one.
The early panel without thumbwheels had multiple valve bases for different configurations of electrode pin outs of the same type of bases. I have nevere seen a book or chart for these but it would not be dificult to draw up a chart of what gos where on the various identical bases & then use the valve data book to test the valve in the correct base?
Paul

[Sparks]

Lawrence, thanks for the link.     I downloaded it in a few seconds!      It is interesting to see that the settings for the valve tester are considerably lower than the actual valve specs from the data book.    That would account for my white hot anode when set to the correct voltages that were, in fact, way too high.     It will be ineteresting to check the valve to see if it still works, because the anode was quite a brilliant white for a second or two before I turned the tester off!
Maybe there is nothing wrong with it after all, and the designers were aware that the volts should be set a lot lower than specified.       I will clean the test switch contacts before putting it together again and testing it with the "real" test volts!    Fortunately, I have a very large number of EF91s, so the probable destruction on one is of no consequence.    
I have heard it suggested that millions of years in the future when the earth is a dying planet, dimly illuminated by a dying sun, and totally bereft of water and life, human or animal, there will still be a sprinkling of EF91s lying in the dried-out wastelands!
Bob

[pwdrive]

Yes, typical operating characteristics given in manufacturers valve data are with a specific -ve grid bias voltage, the two panel tester's grid voltage is fixed at 0.5 volts -ve which is switched to 0.5 volts +ve when doing the mutual conductance test. the maximum cathode current spec for the EF91 is 15mA.

With 250 volts on the anode and 0.5 volts -ve on the grid the cathode current will have exceeded that limit, even more so when the mutual conductance test is done.

Lawrence.

[Sparks]

Thanks for further clarification. Also, I had got it in my head that 1 Volt was applied, not 0.5, so I may not need to clean the switch after all! I have just tested the EF91 that got the white hot anode (In my home-made valve tester) and it is still perfectly OK as far as my humble tester is concerned!
Bob

[pwdrive]

Yes, initially 0.5 volts -ve applied (eg: when adjusting set zero for the meter) 0.5 volts +ve is applied when doing the mutual conductance test, that equals a change in grid/cathode potential of 1 volt, so mA per volt can be read directly from the mutual conductance scale.

Lawrence.

[Sparks]

It seems to be working after a fashion. In order to clean the switch, I had to remove the meter movement again. The needle was slightly bent, and I was able to straighten it without doing any damage. It is now exactly on zero when the device is switched off! On trying it again with the EF91 that had got white hot, it is registering at the top of the red, although the valve still works OK in a one valve receiver/tester. I have the settings on 100V, Pen/LF and 5 mA/Volt as shown in the manual. Putting a new, unused EF91 in it, the needle is mid way in the white, where I had expected it to be well into the green. I will try some other valves later. Maybe I should try an older type valve.
Bob

[Sparks]

I just dug out three 6P25 tetrodes - condition unknown. One tested dud, one clocked up 55% and one 95%, so I am inclined to believe it is probably working now. Some valves are not in the manual though, and I am wondering how one would go about testing them?
Bob

[pwdrive]

I just dug out three 6P25 tetrodes - condition unknown.     One tested dud, one clocked up 55% and one 95%, so I am inclined to believe it is probably working now.       Some valves are not in the manual though, and I am wondering how one would go about testing them?  
Bob

So far as I'm aware the 17th edition of the Avo Valve Data Book was the last one to include settings for the two panel tester, the settings data for the valve you want might be in there, worth a look, here's the link:

https://frank.pocnet.net/instruments/AVO...VDM_17.pdf

Lawrence.