Testing EF80 and EF800 Tubes

[shif...@gmail.com]

Hi,

From what I understand, plenty of people were able to test the EF80 tubes. For some reason, I can't get a real read on them. I get about 128mA Ia on the quick test when expecting 10mA.

I have it connected as follows:

Pin 1, 3, 9 = all to Cathode

Pin 2 = Grid

Pine 4 = Heater

Pin 5 = Heater

Pin 7 = Plate

Pin 8 = Screen

For those of you testing, are you connecting pins 1, 3, and 9, or no? If no, how do you have it setup?

Thanks,

Josh

[Hoeberlin]

Hi, Josh,

connection setup looks good to me. Ithink that You have an oscillation Problem. Cables too long? Ferrite Beads?

BR Henning


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[Big Josh]

That's possible. I made a socket adapter with ferrite beads on it to connect the EF800. Maybe I should have used larger beads? On the other hand, it's entirely exposed. Maybe I should make a faraday cage enclosure for the adapter?

Would an oscillation really cause such a problem? I could imagine an oscillation causing some variations or kinks in traces, but more than 10 times the expected plate current?

I'll do a proper trace and see what the results are. I've only done a quick test with this adapter.

Thanks,

Josh

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[Bill van Dijk]

Josh,

 

Oscillations usually result in a distorted graph, below I have posted an example of a heavily oscillating tube, and the same tube when the oscillations are fixed:

 

 

 

As you can see, big difference. What is the solution? Experimentation. Usually adding inductors to the Anode or Cathode wires can solve it. Keep in mind that what fixes one tube, does not always fix the next tube. As a general rule try to keep wires as short as possible.

 

Hope that helps.

 

Bill

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[Big Josh]

I think I'm going to have to test some other tubes and look back to this one. My uTracer was fine with everything else, but this one is goofy. 

Running a similar test as you above, running g from -5 to -1, s = 170, anode stepping 2 to 170 I get a flat line at all voltages for Is and Ia at 129mA. I'll test another tube later to see if my uTracer brain farted or something.

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[Big Josh]

Well, this is frustrating. My uTracer was fine, but now it doesn't work anymore. I tried testing a 12AX7 and got the same results. 128mA currents. Something stupid is going on with my uTracer now.

[Never Mind]

Perhaps go back to basics.

Ronald's calibration process in the uTracer gives a number of easy and good tests to check for proper operation.

I was thinking starting with the test where two 12k resistors were connected from both from cathode with one then to the screen and the other to Anode.

This neatly checks the current measuring and voltage setting hardware in one simple test.

If this test fails then run the voltage set test for screen and anode voltages to see if the voltage setting hardware is causing trouble.

If the above tests passes then on to the grid voltage test.

As the manual is so well written it should be possible by testing one by one using Ronald manual to pinpoint where your uTracer is going wrong.

Good luck.

[Big Josh]

Thanks, I resolved it. My PCB has had issues with traces or pads lifting, and the negative supply IC1 had to be replaced and bodged to work (I could have reused the old one, but the longer leads on the new one made it easier to fix). It was a little weird since it was working fine a few months ago when I used it last. For whatever reason, likely heat, the center pad lifted off completely when trying to test the latest batch of tubes.

Has anybody else had issues with pads or traces lifting?

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